Methods and Agents for the Diagnosis and Treatment of Hepatocellular Carcinoma

ABSTRACT

The present invention relates to methods of diagnosing, and methods of treating, hepatocellular carcinoma in a subject. The invention also relates to polypeptide antagonists of PLVAP proteins, including humanized and chimeric antibodies that specifically bind PLVAP proteins, as well as compositions and kits comprising such polypeptide antagonists.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/197,650, filed on Oct. 29, 2008. The entire teachings of the above application are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Hepatocellular carcinoma (HCC) is the most frequent primary malignancy of the liver and is the fifth most common cancer in humans worldwide. HCC also is the fourth leading cause of cancer-related death (Parkin D M, Bray F, Ferlay J, Pisani P. Estimating the world cancer burden: Globocan 2000. Int J Cancer 2001; 94:153-156). In 1990, the World Health Organization estimated that there were about 430,000 new cases of liver cancer worldwide, and that a similar number of patients died that year as a result of this disease.

The pathogenesis of HCC has been associated with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, as well as cirrhosis-inducing conditions of liver (Bruix J, et al. J Hepatol 35:421-430, 2001; Bruix J, et al. Cancer Cell 5:215-219, 2004). Accordingly, the incidence of HCC is highest in east Asian countries, such as China, Hong Kong, Taiwan, Korea, and Japan, where HBV and HCV infections are most prevalent (Bruix J, et al. Cancer Cell 5:215-219, 2004; Haskell C M. Chapter 46 Liver: Natural History, Diagnosis and Staging in “Cancer Treatment” 5^(th) edition, W. B, Saunders Company, Philadelphia, editors: Haskell C M & Berek J S). However, the incidence of HCC in western countries is steadily increasing (Parkin D M, et al. Int J Cancer 94; 153-156, 2001). Over the past decade in the United States, HCC displayed the second highest increase in incidence, and the highest increase in death rate, of all cancers (Ann Int Med 139:817-823, 2003). Thus, in the United States and throughout the world, HCC is a major cause of mortality and morbidity, and a significant economic burden due to hospital costs and loss of work by people with HCC.

Successful control of HCC requires correct diagnosis of the disease at an early stage of disease progression. However, distinguishing small HCC tumors from other malignant or non-malignant liver diseases, including metastatic tumors, cholangiocarcinoma, focal nodular hyperplasia, dysplastic and regenerating liver nodules, using current techniques, such as imaging studies, needle core biopsy and/or fine needle aspiration, has proven to be challenging (Ferrell L D, et al. Am J Surg Pathol 17:1113-1123, 1993; Horigome H, et al. Hepato-Gatroenterology 47:1659-1662, 2000; Kalar S, et al. Arch Pathol Lab Med 131:1648-1654, 2007; Seki S, et al. Clin Cancer Res 6:3460-3473, 2000). Moreover, attempts to treat HCC therapeutically have been largely unsuccessful (Bruix J, et al. J Hepatol 35:421-430, 2001; Bruix J, et al. Cancer Cell 5:215-219, 2004; Haskell C M. Chapter 46 Liver: Natural History, Diagnosis and Staging in “Cancer Treatment” 5^(th) edition, W. B, Saunders Company, Philadelphia, editors: Haskell C M & Berek J S; Szklaruk J, et al. AJR 180:441-453, 2003). As a result, despite active therapy, the 5-year survival rate of patients with HCC in the U.S. is only 10.5%, which is second in magnitude only to pancreatic cancer (ACS Cancer Facts & Figures (2007)). Thus, there is an urgent need to identify a more reliable marker to differentiate HCC from other liver pathologies and facilitate early detection of this disease. In addition, there is an urgent need to develop new and more-effective therapeutic agents for the treatment of HCC.

SUMMARY OF THE INVENTION

The present invention, in one embodiment, relates to a humanized antibody that specifically binds human Plasmalemma Vesicle-Associated Protein (PLVAP), wherein the antibody comprises at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:66, SEQ ID NO:68, SEQ ID NO:94, SEQ ID NO:96, SEQ ID NO:98, SEQ ID NO:100, SEQ ID NO:102 and a combination thereof; and at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO:64, SEQ ID NO:104, SEQ ID NO:106, SEQ ID NO:108 and a combination thereof.

In another embodiment, the invention relates to a humanized antibody that specifically binds human PLVAP, wherein the antibody comprises at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:74, SEQ ID NO:76, SEQ ID NO:78, SEQ ID NO:80, SEQ ID NO:82, SEQ ID NO:84, SEQ ID NO:86 and a combination thereof; and at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:70, SEQ ID NO:72, SEQ ID NO:88, SEQ ID NO:90, SEQ ID NO:92 and a combination thereof.

In another embodiment, the invention provides a pharmaceutical composition comprising at least one humanized antibody that specifically binds a PLVAP protein (e.g., a human PLVAP protein). In another embodiment, the pharmaceutical composition further comprises a second therapeutic agent, such as a chemotherapeutic agent.

In a further embodiment, the invention relates to an isolated polypeptide that specifically binds human PLVAP, comprising at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:66, SEQ ID NO:68, SEQ ID NO:94, SEQ ID NO:96, SEQ ID NO:98, SEQ ID NO:100, SEQ ID NO:102 and a combination thereof; and at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO:64, SEQ ID NO:104, SEQ ID NO:106, SEQ ID NO:108 and a combination thereof. In another embodiment, the polypeptide is a chimeric antibody.

In an additional embodiment, the invention provides an isolated polypeptide that specifically binds human PLVAP, comprising at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:74, SEQ ID NO:76, SEQ ID NO:78, SEQ ID NO:80, SEQ ID NO:82, SEQ ID NO:84, SEQ ID NO:86 and a combination thereof; and at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:70, SEQ ID NO:72, SEQ ID NO:88, SEQ ID NO:90, SEQ ID NO:92 and a combination thereof. In another embodiment, the polypeptide is a chimeric antibody.

In other embodiments, the invention relates to murine hybridoma KFCC-GY4 (ATCC Patent Deposit Designation PTA-9963), cells thereof, and antibodies produced by murine hybridoma KFCC-GY4.

In yet other embodiments, the invention relates to murine hybridoma KFCC-GY5 (ATCC Patent Deposit Designation PTA-9964), cells thereof, and antibodies produced by murine hybridoma KFCC-GY5.

In yet another embodiment, the invention relates to a method of treating hepatocellular carcinoma (HCC) in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of a humanized antibody that specifically binds PLVAP. In a particular embodiment, the antibody is administered to the subject by intra-arterial infusion (e.g., hepatic arterial infusion, transarterial chemoembolization) and can inhibit tumor formation, tumor growth, tumor vascularization or tumor progression in the liver of the subject. In another embodiment, the PLVAP antagonist is administered in combination with a second therapeutic agent, such as a chemotherapeutic agent.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.

FIG. 1 is a flow chart diagram depicting an algorithm for the identification of genes that show extreme differential expression between tumor and adjacent non-tumorous tissues.

FIG. 2 is a graph depicting PLVAP gene expression intensities in paired HCC (PHCC) and adjacent non-tumorous liver tissue (PN) samples (n=18), as well as unpaired HCC samples (n=82) as determined by mRNA transcript profiling using Affymetrix gene chips.

FIG. 3A is a graph depicting relative PLVAP expression quantities in paired HCC (PHCC) and adjacent non-tumorous liver tissue (PN) samples as determined by Taqman quantitative RT-PCR. PLVAP mRNA levels are significantly higher in HCC relative to non-tumorous liver tissues.

FIG. 3B is a graph depicting PLVAP gene expression intensities in 18 paired HCC (PHCC) and adjacent non-tumorous liver tissue (PN) samples as determined by microarray analysis. PLVAP transcript levels were higher in HCC than in adjacent non-tumorous liver tissue from each individual for all individuals tested except one.

FIGS. 4A and B show the nucleotide sequence (SEQ ID NO:1) and the deduced amino acid sequence (SEQ ID NO:2) of the His-tagged human PLVAP₅₁₋₄₄₂ protein recombinant fusion protein used to generate mouse anti-PLVAP polyclonal antisera.

FIG. 5 is an image of a Western blot depicting the detection of recombinant PLVAP protein before and after thrombin digestion to remove the His tag. Arrows to the left of the blot indicate the locations of His-PLVAP and PLVAP on the blot. The numbers to the left of the blot indicate the positions of molecular weight standards.

FIG. 6A is a graph depicting the presence of significant relative quantities of PLVAP mRNA in HCC endothelial cells obtained by laser-capturing microdissection from two HCC tissue samples (Sample A (black) and Sample B (gray)) as determined by two-step real-time quantitative RT-PCR. Dashed lines represent Taqman quantitative RT-PCR signals from beta-actin mRNA in the same samples used for quantitative RT-PCR of PLVAP mRNA. The results indicate presence of readily measurable PLVAP mRNA in the dissected endothelial cells (solid lines).

FIG. 6B is a graph depicting the absence of significant relative quantities of PLVAP mRNA in cells obtained by laser-capturing microdissection from non-tumorous liver tissue adjacent to HCC tissue in two HCC samples (Sample A (black) and Sample B (gray)) as determined by two-step Taqman real-time quantitative RT-PCR. The results indicate no detectable (solid black line) and barely detectable (solid gray line) PLVAP mRNA in the dissected cells.

FIG. 6C is a graph depicting the relative quantities of PLVAP mRNA in HCC tumor cells obtained by laser-capturing microdissection from two HCC tissue samples (Sample A (black) and Sample B (gray)) as determined by two-step Taqman real-time quantitative RT-PCR. The results indicate presence of very small amounts of PLVAP mRNA (solid lines) in the dissected HCC cells due to unavoidable minor contamination from portion of vascular endothelial cells attached to the dissected HCC cells.

FIG. 7 is a graph depicting anti-PLVAP antibody titer in mouse antiserum raised against recombinant PLVAP₅₁₋₄₄₂ protein as determined by ELISA.

FIGS. 8A-F are images showing sections of formalin-fixed paired HCC (FIGS. 8A,C,E) and adjacent non-tumorous liver tissues (FIGS. 8B,D,F) from three patients with hepatocellular carcinoma that were stained immunohistochemically using anti-PLVAP polyclonal antisera to detect localization of PLVAP protein. Paired tissues are shown in FIGS. 8A,B; FIGS. 8C,D; and FIGS. 8E,F. PLVAP protein, which appears as a brown stain (arrows) in the HCC images, was detected only in capillary endothelial cells of hepatocellular carcinomas (FIGS. 8A,C,E). No detectable PLVAP was present in non-tumorous liver tissue (FIGS. 8B,D,F).

FIGS. 9A-F are images showing sections of formalin-fixed HCC (FIGS. 9A,C,E,F) and non-tumorous liver tissues (FIGS. 9B,D) from three additional patients with hepatocellular carcinoma that were stained immunohistochemically using anti-PLVAP polyclonal antisera to detect localization of PLVAP protein. FIGS. 9A,B and FIGS. 9C,D show paired tissue samples of HCC and adjacent non-tumorous liver tissue. PLVAP protein, which appears as a brown stain (arrows) in the HCC images, was detected only in capillary endothelial cells of hepatocellular carcinomas (FIGS. 9A,C,E,F). No detectable PLVAP was present in non-tumorous liver tissue (FIGS. 9B,D).

FIGS. 10A-F are images showing sections of formalin-fixed focal nodular hyperplasia tissues from six different patients that were stained immunohistochemically using anti-PLVAP polyclonal antisera to detect localization of PLVAP protein. PLVAP protein was not detected in endothelial cells lining the vascular sinusoids/capillary of non-tumorous liver tissues of focal nodular hyperplasia. Some positive staining (dark gray) was noted in epithelial cells of bile ducts (FIGS. 10A, 10D and 10F) and vessels of portal tracts (FIGS. 10D and 10F), but not in the endothelial cells of liver parenchyma. The positive staining of bile duct epithelial cells was due to binding of non-specific antibodies in the PLVAP antiserum.

FIGS. 11A and 11B are images showing sections of formalin-fixed tissue from two patients with hepatic hemangioma that were stained immunohistochemically with anti-PLVAP polyclonal antiserum. Endothelial lining cells of hepatic hemangioma did not show significant expression of PLVAP protein.

FIGS. 12A and 12B are images showing sections of formalin-fixed tissue from two patients with chronic active hepatitis B that were stained immunohistochemically with anti-PLVAP polyclonal antiserum. PLVAP protein was not detected in endothelial cells lining the vascular sinusoids/capillary of non-tumorous liver tissues from chronic hepatitis B patients.

FIGS. 13A-D are images showing sections of formalin-fixed tissue from three different patients with chronic active hepatitis C that were stained immuno-histochemically with anti-PLVAP polyclonal antiserum. The tissue sections shown in FIGS. 13B and 13D are from the same patient. PLVAP protein was not detected in endothelial cells lining the vascular sinusoids/capillary of non-tumorous liver tissues from chronic hepatitis C patients.

FIGS. 14A-D are images showing sections of formalin-fixed tissue from three different patients with metastatic liver cancers that were stained immunohistochemically with anti-PLVAP polyclonal antiserum. The tissue sections are from patients with metastatic colorectal adenocarcinoma (FIG. 14A), intrahepatic cholangiocarcinoma (FIGS. 14B and C) or metastatic ovarian carcinoma (FIG. 14D). The tissue sections shown in FIGS. 14B and 14C are from the same patient. PLVAP protein was not detected in endothelial cells lining the vascular sinusoids/capillary of metastatic cancer tissues.

FIG. 15A shows the nucleotide gene (top) (SEQ ID NO:3) and deduced amino acid (middle) (SEQ ID NO:4) sequences of the V_(H) domain of monoclonal antibody KFCC-GY4. The sequence of amino acid residues in CDRs 1 (SEQ ID NO:5), 2 (SEQ ID NO:6) and 3 (SEQ ID NO:7) also are indicated (bottom).

FIG. 15B shows the nucleotide gene (top) (SEQ ID NO:8) and deduced amino acid (middle) (SEQ ID NO:9) sequences of the V_(L) domain of monoclonal antibody KFCC-GY4. The sequence of amino acid residues in CDRs 1 (SEQ ID NO:10), 2 (SEQ ID NO:11) and 3 (SEQ ID NO:12) also are indicated (bottom).

FIG. 16A shows the nucleotide gene (top) (SEQ ID NO:13) and deduced amino acid (middle) (SEQ ID NO:14) sequences of the V_(H) domain of monoclonal antibody KFCC-GY5. The sequence of amino acid residues in CDRs 1 (SEQ ID NO:15), 2 (SEQ ID NO:16) and 3 (SEQ ID NO:17) also are indicated (bottom).

FIG. 16B shows the nucleotide gene (top) (SEQ ID NO:18) and deduced amino acid (middle) (SEQ ID NO:19) sequences of the V_(L) domain of monoclonal antibody KFCC-GY5. The sequence of amino acid residues in CDRs 1 (SEQ ID NO:20), 2 (SEQ ID NO:21) and 3 (SEQ ID NO:22) also are indicated (bottom).

FIG. 17 is a graph depicting the binding of KFCC-GY4 (open circles) and KFCC-GY5 (filled circles) monoclonal antibodies to recombinant PLVAP protein at various antibody concentrations, as determined by ELISA.

FIG. 18 is an immunoblot showing that KFCC-GY4 and KFCC-GY5 monoclonal antibodies can detect 5 ng of recombinant PLVAP protein. Lane 1: molecular weight standard; Lane 2: immunoblot with KFCC-GY4 monoclonal antibody; Lane 3: immunoblot with KFCC-GY5 monoclonal antibody. The molecular weight of recombinant PLVAP protein is 45 kD.

FIGS. 19A and 19C are Coomassie blue-stained SDS acrylamide gels. Lane 1: molecular weight standard; Lane 2: hydrophobic membrane proteins extracted with TX-114 from human umbilical cord vascular endothelial cells that had been stimulated with VEGF (40 ng/ml) for 72 hours before extraction.

FIG. 19B is an immunoblot, wherein the extract shown in Lane 2 of FIG. 19A was probed with KFCC-GY4 monoclonal antibodies. Lane 1: molecular weight standard; Lane 2: hydrophobic membrane proteins extracted with TX-114 from human umbilical cord vascular endothelial cells that had been stimulated with VEGF (40 ng/ml) for 72 hours before extraction.

FIG. 19D is an immunoblot, wherein the extract shown in Lane 2 of FIG. 19C was probed with KFCC-GY-5 monoclonal antibodies. Lane 1: molecular weight standard; Lane 2: hydrophobic membrane proteins extracted with TX-114 from human umbilical cord vascular endothelial cells that had been stimulated with VEGF (40 ng/ml) for 72 hours before extraction.

FIG. 20A is a fluorescence micrograph depicting immunofluorescence staining of human vascular endothelial cells (HUVEC) with control normal mouse IgG. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI). Magnification=600×.

FIG. 20B is a fluorescence micrograph depicting immunofluorescence staining of human vascular endothelial cells (HUVEC) with monoclonal antibody to von Willebrand factor (VWF). VWF is a positive marker for human vascular endothelial cells. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI). Magnification=600×.

FIG. 20C is a fluorescence micrograph depicting immunofluorescence staining of human vascular endothelial cells (HUVEC) with KFCC-GY4 monoclonal antibody to PLVAP. KFCC-GY4 monoclonal anti-PLVAP antibodies reacted positively with human vascular endothelial cells. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI). Magnification=600×.

FIG. 20D is a fluorescence micrograph depicting immunofluorescence staining of human vascular endothelial cells (HUVEC) with KFCC-GY5 monoclonal antibody to PLVAP. KFCC-GY5 monoclonal anti-PLVAP antibodies reacted positively with human vascular endothelial cells. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI). Magnification=600×.

FIG. 21A is a light micrograph of a section of formalin-fixed hepatoma tissue embedded in a paraffin block, which was stained with KFCC-GY5 monoclonal anti-PLVAP antibodies. A strong PLVAP signal (dark gray stain) was detected in vascular endothelial cells of hepatoma. Magnification is 100×.

FIG. 21B is a light micrograph of a section of formalin-fixed hepatoma tissue from the same patient as the sample shown in FIG. 21A, which was stained with KFCC-GY4 monoclonal anti-PLVAP antibodies. A moderate PLVAP signal (light gray stain) was detected in vascular endothelial cells of hepatoma. Magnification is 100×.

FIG. 21C is a light micrograph of a section of formalin-fixed hepatoma tissue from a different patient than the samples shown in FIGS. 21A and B, which was stained with KFCC-GY5 monoclonal anti-PLVAP antibodies. A strong PLVAP signal (dark gray stain) was detected in vascular endothelial cells. Magnification is 100×.

FIG. 21D is a light micrograph of a section of formalin-fixed hepatoma tissue from the same patient as the sample shown in FIG. 21C embedded in a paraffin block, which was stained with KFCC-GY4 monoclonal anti-PLVAP antibodies. A moderate PLVAP signal (light gray stain) was detected in vascular endothelial cells, indicating that KFCC-GY4 monoclonal antibodies bind the PLVAP antigen less well than KFCC-GY5 antibodies. Magnification is 100×.

FIGS. 22A-H are light micrographs of sections of hepatoma tissues (FIGS. 22A, C, E, and G) and adjacent non-tumorous liver tissues (FIGS. 22B, D, F, and H) from four different randomly selected hepatoma patients. The sections were stained with KFCC-GY5 monoclonal anti-PLVAP antibodies. PLVAP signal (gray stain) was detected in vascular endothelial cells of hepatoma tissue, but not in vascular endothelial cells non-tumorous liver tissue. Magnification is 100×. FIGS. 22A and B, C and D, E and F, and G and H represent the four sets of paired hepatoma and non-tumorous liver tissues.

FIG. 23A is a fluorescence micrograph depicting human vascular endothelial cells (HUVECs) that were stained with control mouse IgG. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI).

FIG. 23B is a fluorescence micrograph depicting human vascular endothelial cells (HUVECs) that were stained with KFCC-GY4 monoclonal antibody to PLVAP. KFCC-GY4 monoclonal anti-PLVAP antibodies reacted positively with the surfaces of the human vascular endothelial cells. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI).

FIG. 23C is a fluorescence micrograph depicting human vascular endothelial cells (HUVECs) that were stained with KFCC-GY5 monoclonal antibody to PLVAP. KFCC-GY5 monoclonal anti-PLVAP antibodies reacted positively with the surfaces of the human vascular endothelial cells. Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI).

FIG. 24 shows the amino acid sequence of human PLVAP protein (Genbank Accession No. NP_(—)112600; SEQ ID NO:23).

FIGS. 25A and 25B show the nucleotide sequence of full-length human PLVAP cDNA (Genbank Accession No. NM_(—)031310; SEQ ID NO:24).

FIG. 26 is a table indicating PLVAP expression in vascular endothelial cells in various normal tissues and organs in humans and two non-human primates, as determined by immunohistochemistry using KFCC-GY4 and Gy5 antibodies.

FIGS. 27A-F2 show normal human and monkey tissues that were immunohistochemically stained with KFCC-GY4, KFCC-GY5 and anti-CD34 monoclonal antibodies (mAbs). Arrows point to capillary endothelial cells that express PLVAP in the respective tissues.

FIG. 27A shows a section of human adrenal gland tissue that has been stained with the KFCC-GY4 mAb. FIG. 27B shows a section of human adrenal gland tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. FIG. 27C shows a section of adrenal gland tissue from cynomolgus monkey that has been stained with the KFCC-GY4 mAb. FIG. 27D shows a section of adrenal gland tissue from rhesus monkey that has been stained with the KFCC-GY4 mAb.

FIG. 27E shows a section of human adrenal gland tissue that has been stained with the KFCC-GY5 mAb. FIG. 27F shows a section of human adrenal gland tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. FIG. 27G shows a section of adrenal gland tissue from cynomolgus monkey that has been stained with the KFCC-GY5 mAb. FIG. 27H shows a section of adrenal gland tissue from rhesus monkey that has been stained with the KFCC-GY5 mAb.

FIG. 27I shows a section of human kidney tissue that has been stained with the KFCC-GY4 mAb. FIG. 27J shows a section of human kidney tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. FIG. 27K shows a section of kidney tissue from cynomolgus monkey that has been stained with the KFCC-GY4 mAb. FIG. 27L shows a section of kidney tissue from rhesus monkey that has been stained with the KFCC-GY4 mAb. KFCC-GY4 mAb stains capillary endothelial cells between renal tubules and does not stain endothelial cells in glomeruli. In contrast, Anti-CD34 antibody stains positively capillary endothelial cells between renal tubules and in glomeruli.

FIG. 27M shows a section of human kidney tissue that has been stained with the KFCC-GY5 mAb. FIG. 27N shows a section of human kidney tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. FIG. 27O shows a section of kidney tissue from cynomolgus monkey that has been stained with the KFCC-GY5 mAb. FIG. 27P shows a section of kidney tissue from rhesus monkey that has been stained with the KFCC-GY5 mAb. Like KFCC-GY4 mAb, KFCC-GY5 mAb stains capillary endothelial cells between renal tubules and does not stain endothelial cells in glomeruli. In contrast, Anti-CD34 antibody stains positively capillary endothelial cells between renal tubules and in glomeruli.

FIG. 27Q shows a section of human brain tissue that has been stained with the KFCC-GY4 mAb. FIG. 27R shows a section of human brain tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. Vascular endothelial cells of brain stained positively for CD34 endothelial marker (arrows). FIG. 27S shows a section of brain tissue from cynomolgus monkey that has been stained with the KFCC-GY4 mAb. FIG. 27T shows a section of brain tissue from rhesus monkey that has been stained with the KFCC-GY4 mAb. Both human and monkey brain endothelial cells do not express PLVAP.

FIG. 27U shows a section of human brain tissue that has been stained with the KFCC-GY5 mAb. FIG. 27V shows a section of human brain tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. Vascular endothelial cells of brain are stained positively for CD34 endothelial marker (arrows). FIG. 27W shows a section of brain tissue from cynomolgus monkey that has been stained with the KFCC-GY5 mAb. FIG. 27X shows a section of brain tissue from rhesus monkey that has been stained with the KFCC-GY5 mAb. Both human and monkey brain endothelial cells do not express PLVAP.

FIG. 27Y shows a section of human liver tissue that has been stained with the KFCC-GY4 mAb. FIG. 27Z shows a section of human liver tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. Vascular endothelial cells of brain stained positively for CD34 endothelial marker (arrows). FIG. 27A2 shows a section of liver tissue from cynomolgus monkey that has been stained with the KFCC-GY4 mAb. FIG. 27B2 shows a section of liver tissue from rhesus monkey that has been stained with the KFCC-GY4 mAb. KFCC-GY4 mAb does not react with endothelial cells of liver sinusoid (thin arrows) and central vein (thick arrows) in human, cynomolgus monkey and rhesus monkey.

FIG. 27C2 shows a section of human liver tissue that has been stained with the KFCC-GY5 mAb. FIG. 27D2 shows a section of human liver tissue that has been stained with the anti-human CD34 mAb, which recognizes CD34, a marker for endothelial cells. Vascular endothelial cells of brain stained positively for CD34 endothelial marker (arrows). FIG. 27E2 shows a section of liver tissue from cynomolgus monkey that has been stained with the KFCC-GY4 mAb. FIG. 27F2 shows a section of liver tissue from rhesus monkey that has been stained with the KFCC-GY5 mAb. KFCC-GY5 mAb does not react with endothelial cells of liver sinusoid (thin arrows) and central vein (thick arrows) in human, cynomolgus monkey and rhesus monkey.

FIG. 28A shows a Coomassie blue-stained SDS-PAGE gel of total protein extract from 1×10⁸ E. coli expressing His-tagged PLVAP51-442 (Lane 1); His-tagged PLVAP282-442 (Lane 2); His-tagged PLVAP51-292 (Lane 3); or His-tagged CEACAM6 (Lane 4). Molecular weight protein standards are resolved in Lane M.

FIG. 28B shows an immunoblot that was probed with mouse KFCC-GY4 mAb to detect PLVAP proteins in total protein extract from 1×10⁸ E. coli expressing His-tagged PLVAP51-442 (Lane 1); His-tagged PLVAP282-442 (Lane 2); His-tagged PLVAP51-292 (Lane 3); or His-tagged CEACAM6 (Lane 4). Molecular weight protein standards are resolved in Lane M.

FIG. 28C shows an immunoblot that was probed with mouse KFCC-GY5 mAb to detect PLVAP proteins in total protein extract from 1×10⁸ E. coli expressing His-tagged PLVAP51-442 (Lane 1); His-tagged PLVAP282-442 (Lane 2); His-tagged PLVAP51-292 (Lane 3); or His-tagged CEACAM6 (Lane 4). Molecular weight protein standards are resolved in Lane M.

FIG. 28D shows an immunoblot that was probed with anti-His tag antibody to detect His-tagged PLVAP proteins in total protein extract from 1×10⁸ E. coli expressing His-tagged PLVAP51-442 (Lane 1); His-tagged PLVAP282-442 (Lane 2); His-tagged PLVAP51-292 (Lane 3); or His-tagged CEACAM6 (Lane 4). Molecular weight protein standards are resolved in Lane M.

FIG. 29 is a bar graph showing binding of KFCC-GY4 monoclonal antibody (mAb) to PLVAP that was captured first by KFCC-GY5 mAb. ELISA was used for the study. Each value is a mean of duplicates.

FIG. 30 is a bar graph depicting additive binding of fully humanized composite monoclonal antibodies derived from KFCC-GY4 (CSR01-VH5/VK2) and KFCC-GY5 (CAS02-VH5/VK3) to PLVAP protein. The values are an average of duplicates.

FIG. 31 shows a Coomassie blue-stained SDS-PAGE gel of protein-A purified chimeric KFCC-GY4 and KFCC-GY5 antibodies after reduction of disulfide bonds. Lane 1: Precision plus protein standards (Bio-Rad); Lane 2: 1.0 μg chimeric KFCC-GY4 antibody; Lane 3: 1.0 μg chimeric KFCC-GY5 antibody; Lane 4: Precision plus protein standards (Bio-Rad).

FIGS. 32A-G show the nucleotide sequence of the pANT12-based plasmid vector encoding the KFCC-GY4 VK Chimera and the deduced amino acid sequence of the chimera.

FIGS. 33A-D show the nucleotide sequence of the pANT13-based plasmid vector encoding the KFCC-GY4 VK Chimera and the deduced amino acid sequence of the chimera.

FIGS. 34A-F show the nucleotide sequence of the pANT12-based plasmid vector encoding the KFCC-GY5 VK Chimera and the deduced amino acid sequence of the chimera.

FIGS. 35A-D show the nucleotide sequence of the pANT13-based plasmid vector encoding the KFCC-GY5 VK Chimera and the deduced amino acid sequence of the chimera.

FIG. 36 is a graph depicting the results of a KFCC-GY4 antibody competition ELISA in which a dilution series of chimeric and murine KFCC-GY4 antibodies were tested against a fixed concentration of biotinylated-GY4 for binding to PLVAP. Binding of biotinylated antibody decreases with increasing amounts of chimeric and control murine antibodies.

FIG. 37 is a graph depicting the results of a KFCC-GY5 antibody competition ELISA in which a dilution series of chimeric and murine KFCC-GY5 antibodies were tested against a fixed concentration of biotinylated-GY5 for binding to PLVAP. Binding of biotinylated antibody decreases with increasing amounts of chimeric and control murine antibodies.

FIGS. 38A-E show the nucleotide and amino acid sequences of the variable domains of heavy and light chains from the humanized antibodies derived from chimeric KFCC-GY4 antibody CSR01. FIG. 38A shows the nucleotide and amino acid sequences of the kappa light chain CSR01-VK1 (SEQ ID NOS:59 and 60). FIG. 38B shows the nucleotide and amino acid sequences of the kappa light chain CSR01-VK2 (SEQ ID NOS:61 and 62). FIG. 38C shows the nucleotide and amino acid sequences of the kappa light chain CSR01-VK3 (SEQ ID NOS:63 and 64). FIG. 38D shows the nucleotide and amino acid sequences of the heavy chain CSR01-VH4 (SEQ ID NOS:65 and 66). FIG. 38E shows the nucleotide and amino acid sequences of the heavy chain CSR01-VH5 (SEQ ID NOS:67 and 68). The amino acid sequences of the CDRs are underlined. The amino acids that are altered to reduce potential antigenicity are shown in a square box.

FIGS. 39A-D show the nucleotide and amino acid sequences of the variable domains of heavy and light chains from the humanized antibodies derived from chimeric KFCC-GY5 antibody CSR02. FIG. 39A shows the nucleotide and amino acid sequences of the kappa light chain CSR02-VK2 (SEQ ID NOS:69 and 70). FIG. 39B shows the nucleotide and amino acid sequences of the kappa light chain CSR02-VK3 (SEQ ID NOS:71 and 72). FIG. 39C shows the nucleotide and amino acid sequences of the heavy chain CSR02-VH4 (SEQ ID NOS:73 and 74). FIG. 39E shows the nucleotide and amino acid sequences of the heavy chain CSR02-VH5 (SEQ ID NOS:75 and 76). The amino acid sequences of the CDRs are underlined. The amino acids that are altered to reduce potential antigenicity are shown in a square box.

FIG. 40 is a flowchart diagram depicting the derivation of fully humanized anti-human PLVAP composite monoclonal antibodies (mAb) from murine KFCC-GY4 and KFCC-GY5 mAbs.

FIG. 41A depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable heavy chain VH variant 1 (SEQ ID NOS:77 and 78). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are underlined.

FIG. 41B depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable heavy chain VH variant 2 (SEQ ID NOS:79 and 80). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 41C depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable heavy chain VH variant 3 (SEQ ID NOS:81 and 82). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 41D depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable heavy chain VH variant 4 (SEQ ID NOS:83 and 84). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 41E depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable heavy chain VH variant 5 (SEQ ID NOS:85 and 86). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 42A depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable light chain VK variant 1 (SEQ ID NOS:87 and 88). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 42B depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable light chain VK variant 2 (SEQ ID NOS:89 and 90). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 42C depicts the nucleotide and deduced amino acid sequences of the KFCC-GY5 variable light chain VK variant 3 (SEQ ID NOS:91 and 92). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 43A depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable heavy chain VH variant 1 (SEQ ID NOS:93 and 94). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 43B depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable heavy chain VH variant 2 (SEQ ID NOS:95 and 96). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 43C depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable heavy chain VH variant 3 (SEQ ID NOS:97 and 98). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 43D depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable heavy chain VH variant 4 (SEQ ID NOS:99 and 100). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 43E depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable heavy chain VH variant 5 (SEQ ID NOS:101 and 102). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 44A depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable light chain VK variant 1 (SEQ ID NOS:103 and 104). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 44B depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable light chain VK variant 2 (SEQ ID NOS:105 and 106). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIG. 44C depicts the nucleotide and deduced amino acid sequences of the KFCC-GY4 variable light chain VK variant 3 (SEQ ID NOS:107 and 108). CDR nucleotide and protein sequences are lightly shaded. Variant amino acids changed from the original hybridoma sequence are are underlined.

FIGS. 45A-B show an alignment of variable domain sequences of humanized KFCC-GY4 antibody variant heavy chains and Kappa light chains.

FIGS. 46A-B show an alignment of variable domain sequences of humanized KFCC-GY5 antibody variant heavy chains and Kappa light chains.

FIG. 47A shows a Coomassie Blue-stained SDS-PAGE gel of purified humanized KFCC-GY4 antibodies after reduction of disulfide bonds. Lane 1 Precision Plus marker (Biorad); Lane 2 1.0 μg VH4/VK2 IgG4; Lane 3 1.0 μg VH4/VK3 IgG4; Lane 4 1.0 μg VH5/VK1 IgG4; Lane 5 1.0 μg VH5/VK2 IgG4; Lane 6 1.0 μg VH5/VK3 IgG4; Lane 7 Precision Plus marker.

FIG. 47B shows a Coomassie Blue-stained SDS-PAGE gel of purified humanized KFCC-GY5 antibodies after reduction of disulfide bonds. Lane 1 Precision Plus marker; Lane 2 1.0 μg VH4/VK2 IgG4; Lane 3 1.0 μg VH4/VK3 IgG4; Lane 4 1.0 μg VH5/VK2 IgG4; Lane 5 1.0 μg VH5/VK3 IgG4; Lane 6 Precision Plus marker.

FIG. 48 is a graph depicting the results of a PLVAP competition ELISA illustrating the binding of purified variant KFCC-GY4 humanized antibodies that were mixed with a fixed concentration of competitor biotinylated-murine KFCC-GY4 antibody to PLVAP protein at varying concentrations.

FIG. 49 is a graph depicting the results of a PLVAP competition ELISA illustrating the binding of purified variant KFCC-GY5 humanized antibodies that were mixed with a fixed concentration of competitor KFCC-GY5 antibody to PLVAP protein at varying concentrations.

FIG. 50 depicts a titration curve illustrating binding of both chimeric and fully humanized composite anti-PLVAP monoclonal antibodies to PLVAP, as determined by ELISA.

FIGS. 51A-C are images of human umbilical cord vascular endothelial cells that have been stained with murine KFCC-GY4 and KFCC-GY5 monoclonal antibodies in immunofluorescence studies. FIG. 51A shows immunofluorescence staining of human umbilical cord vascular endothelial cells with murine KFCC-GY4 mAbs. FIG. 51B shows immunofluorescence staining of human umbilical cord vascular endothelial cells with murine KFCC-GY5 mAbs. FIG. 51C shows immunofluorescence staining of human umbilical cord vascular endothelial cells with mouse IgG as a negative control.

FIGS. 52A-G are images of human umbilical cord vascular endothelial cells that have been stained with chimeric or humanized KFCC-GY4 (CSR01) antibodies in immunofluorescence studies. FIG. 52A: chimeric KFCC-GY4 mAb; FIG. 52B: CSR01-VH4/VK2; FIG. 52C: CSR01-VH4/VK3; FIG. 52D: CSR01-VH5/VK1; FIG. 52E: CSR01-VH5/VK2; FIG. 52F: CSR01-VH5/VK3; FIG. 52G: human IgG.

FIGS. 53A-F are images of human umbilical cord vascular endothelial cells that have been stained with chimeric or humanized KFCC-GY5 antibodies in immunofluorescence studies. FIG. 53A: chimeric KFCC-GY5 (CSR02) mAb; FIG. 53B: CSR02-VH4/VK2; FIG. 53C: CSR02-VH4/VK3; FIG. 53D: CSR02-VH5/VK2; FIG. 53E: CSR02-VH5/VK3; FIG. 53F: human IgG.

FIG. 54 is a graph depicting the detection of PLVAP protein in two HCC patient serum samples and in serially diluted PLVAP standards (1000 ng/ml to 10 ng/ml). No PLVAP was detected in two normal serum samples. Serum samples were obtained from two patients with hepatocellular carcinoma (HCC-63 and HCC-82) and two normal adults (Normal-13 and Normal-14). Serum samples were assayed at 2-fold and 4-fold dilutions.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

Definitions

As used herein, the terms “Plasmalemma Vesicle-Associated Protein,” “PLVAP,” and “PV-1” refer to a naturally occurring or endogenous PLVAP (e.g., mammalian, human) protein, and to proteins having an amino acid sequence that is the same or substantially the same as that of naturally occurring or endogenous PLVAP protein (e.g., recombinant proteins, synthetic proteins). Accordingly, the terms “Plasmalemma Vesicle-Associated Protein,” “PLVAP,” and “PV-1”, which are used interchangeably herein, include polymorphic or allelic variants and other isoforms of a PLVAP protein produced by, e.g., alternative splicing or other cellular processes, that occur naturally in mammals (e.g., humans). Preferably, the PLVAP protein is a human protein that has the amino acid sequence of SEQ ID NO:23 (See, Genbank Accession No. NP_(—)112600 and FIG. 24).

As defined herein, a “PLVAP antagonist” is an agent (e.g., antibody, small molecule, peptide, peptidomimetic, nucleic acid) that, in one embodiment, inhibits (e.g., reduces, prevents) an activity of a PLVAP protein; or, in another embodiment, inhibits (e.g., reduces, prevents) the expression of a PLVAP gene and/or gene product. Activities of a PLVAP protein that can be inhibited by an antagonist of the invention include, but are not limited to, formation, growth, vascularization and/or progression of a hepatocellular carcinoma tumor. In a particular, embodiment, the PLVAP antagonist specifically binds a mammalian (e.g., human) PLVAP protein and inhibits an activity of the PLVAP protein.

As used herein, “specifically binds” refers to binding of an agent (e.g., an antibody) to a PLVAP gene product (e.g., RNA, protein) with an affinity (e.g., a binding affinity) that is at least about 5 fold, preferably at least about 10 fold, greater than the affinity with which the PLVAP antagonist binds a non-PLVAP protein.

As used herein, the term “polypeptide” refers to a polymer of amino acids, and not to a specific length. Thus, “polypeptide” encompasses proteins, peptides, and oligopeptides.

As used herein, the term “antibody” refers to a polypeptide having affinity for a target, antigen, or epitope, and includes both naturally-occurring and engineered antibodies. The term “antibody” encompasses polyclonal, monoclonal, human, chimeric, humanized, primatized, veneered, and single chain antibodies, as well as fragments of antibodies (e.g., Fv, Fc, Fd, Fab, Fab′, F(ab′), scFv, scFab, dAb). (See e.g., Harlow et al., Antibodies A Laboratory Manual, Cold Spring Harbor Laboratory, 1988).

The term “antibody variable region” refers to the region of an antibody that specifically binds an epitope (e.g., V_(H), V_(HH), V_(L)), either independently or when combined with other antibody variable regions (e.g., a V_(H)/V_(L) pair).

The term “epitope” refers to a unit of structure conventionally bound by an antibody V_(H)/V_(L) pair. An epitope defines the minimum binding site for an antibody and, thus, represents the target of specificity of an antibody.

The term “complementarity determining region” or “CDR” refers to a hypervariable region of an antibody variable region from a heavy chain or light chain, which contains amino acid sequences capable of specifically binding to an antigenic target (e.g., epitope). A typical heavy or light chain will have three CDRs (CDR1, CDR2, CDR3), which account for the specificity of the antibody for a particular epitope.

As defined herein, the term “antigen binding fragment” refers to a portion of an antibody that contains one or more CDRs and has affinity for an antigenic determinant by itself. Non-limiting examples include Fab fragments, F(ab)′₂ fragments, heavy-light chain dimers, and single chain structures, such as a complete light chain or a complete heavy chain.

As used herein, the term “specificity” refers to the ability of an antibody to bind preferentially to an epitope, and does not necessarily imply high affinity.

The term “affinity” refers to a measure of the binding strength between an antibody and an antigenic determinant. Affinity depends on a number of factors, including the closeness of stereochemical fit between the antibody and antigenic determinant, the size of the area of contact between them, and the distribution of charged and hydrophobic groups.

As used herein, the term “affinity constant” or “K_(d)” refers to a dissociation constant used to measure the affinity of an antibody for an antigen. The lower the affinity constant, the higher the affinity of the immunoglobulin for the antigen or antigenic determinant and vice versa. Such a constant is readily calculated from the rate constants for the association-dissociation reactions as measured by standard kinetic methodology for antibody reactions.

As referred to herein, the term “competes” means that the binding of a first polypeptide (e.g., antibody) to a target antigen is inhibited by the binding of a second polypeptide (e.g., antibody). For example, binding may be inhibited sterically, for example by physical blocking of a binding domain or by alteration of the structure or environment of a binding domain such that its affinity or avidity for a target is reduced.

As used herein, the term “peptide” refers to a compound consisting of from about 2 to about 100 amino acid residues wherein the amino group of one amino acid is linked to the carboxyl group of another amino acid by a peptide bond. Such peptides are typically less than about 100 amino acid residues in length and preferably are about 10, about 20, about 30, about 40 or about 50 residues.

As used herein, the term “peptidomimetic” refers to molecules which are not peptides or proteins, but which mimic aspects of their structures. Peptidomimetic antagonists can be prepared by conventional chemical methods (see e.g., Damewood J. R. “Peptide Mimetic Design with the Aid of Computational Chemistry” in Reviews in Computational Biology, 2007, Vol. 9, pp. 1-80, John Wiley and Sons, Inc., New York, 1996; Kazmierski W. K., “Methods of Molecular Medicine: Peptidomimetic Protocols,” Humana Press, New Jersey, 1999).

The terms “hepatocellular carcinoma,” “HCC,” and “hepatoma” are used interchangeably herein to refer to cancer that arises from hepatocytes, the major cell type of the liver.

As defined herein, “therapy” is the administration of a particular therapeutic or prophylactic agent to a subject (e.g., a mammal, a human), which results in a desired therapeutic or prophylactic benefit to the subject.

As defined herein, a “therapeutically effective amount” is an amount sufficient to achieve the desired therapeutic or prophylactic effect under the conditions of administration, such as an amount sufficient to inhibit (i.e., reduce, prevent) tumor formation, tumor growth (proliferation, size), tumor vascularization and/or tumor progression (invasion, metastasis) in the liver of a patient with HCC. The effectiveness of a therapy (e.g., the reduction/elimination of a tumor and/or prevention of tumor growth) can be determined by any suitable method (e.g., in situ immunohistochemistry, imaging (ultrasound, CT scan, MRI, NMR), ³H-thymidine incorporation).

As defined herein a “treatment regimen” is a regimen in which one or more therapeutic or prophylactic agents are administered to a mammalian subject at a particular dose (e.g., level, amount, quantity) and on a particular schedule or at particular intervals (e.g., minutes, days, weeks, months).

As used herein, a “subject” refers to a mammalian subject. The term “mammalian subject” is defined herein to include mammals such as primates (e.g., humans), cows, sheep, goats, horses, dogs cats, rabbits, guinea pigs, rats, mice or other bovine, ovine, equine, canine feline, rodent or murine species. Examples of suitable subjects include, but are not limited to, human patients who have, or are at risk for developing, HCC. Examples of high-risk groups for the development of HCC include individuals with chronic hepatitis infection (hepatitis B, hepatitis C) and individuals who have cirrhosis of the liver or related hepatic conditions.

The terms “prevent,” “preventing,” or “prevention,” as used herein, mean reducing the probability/likelihood or risk of HCC tumor formation or progression by a subject, delaying the onset of a condition related to HCC in the subject, lessening the severity of one or more symptoms of an HCC-related condition in the subject, or any combination thereof. In general, the subject of a preventative regimen most likely will be categorized as being “at-risk”, e.g., the risk for the subject developing HCC is higher than the risk for an individual represented by the relevant baseline population.

As used herein, the terms “treat,” “treating,” or “treatment,” mean to counteract a medical condition (e.g., a condition related to HCC) to the extent that the medical condition is improved according to a clinically-acceptable standard (e.g., reduced number and/or size of HCC tumors in a subject's liver).

As used herein, the terms “low stringency,” “medium stringency,” “high stringency,” or “very high stringency conditions” describe conditions for nucleic acid hybridization and washing. Guidance for performing hybridization reactions can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6, which is incorporated herein by reference in its entirety. Aqueous and nonaqueous methods are described in that reference and either can be used. Specific hybridization conditions referred to herein are as follows: (1) low stringency hybridization conditions in 6× sodium chloride/sodium citrate (SSC) at about 45° C., followed by two washes in 0.2×SSC, 0.1% SDS at least at 50 C (the temperature of the washes can be increased to 55° C. for low stringency conditions); (2) medium stringency hybridization conditions in 6×SSC at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 60 C; (3) high stringency hybridization conditions in 6×SSC at about 45° C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 65° C.; and preferably (4) very high stringency hybridization conditions are 0.5M sodium phosphate, 7% SDS at 65° C., followed by one or more washes at 0.2×SSC, 1% SDS at 65° C. Very high stringency conditions (4) are the preferred conditions and the ones that should be used unless otherwise specified.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art (e.g., in cell culture, molecular genetics, nucleic acid chemistry, hybridization techniques and biochemistry). Standard techniques are used for molecular, genetic and biochemical methods (see generally, Sambrook et al., Molecular Cloning: A Laboratory Manual, 2d ed. (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. and Ausubel et al., Short Protocols in Molecular Biology (1999) 4_(th) Ed, John Wiley & Sons, Inc. which are incorporated herein by reference) and chemical methods.

PLVAP

Plasmalemma vesicle-associated protein (PLVAP), also known as PV1, is a type II integral membrane glycoprotein whose expression is restricted to certain vascular endothelial cells (Mol Biol Cell 15:3615-3630 (2004)). PLVAP has been shown to be a key structural component of fenestral and stomatal diaphragms of fenestrated endothelia Id. In addition, PLVAP expression is necessary for the formation of endothelial fenestral diaphragms and may be involved in modulating endothelial permeability and transport (Am J Physiol Heart Circ Physiol 286:H1347-1353, 2004). The genomic organization of human PLVAP gene has been reported (Stan R V, Arden K C, Palade G E. cDNA and protein sequence, genomic organization, and analysis of cis regulatory elements of mouse and human PLVAP genes. Genomics 72; 304-313, 2001).

As described herein, the inventors have demonstrated that PLVAP gene expression is significantly elevated in hepatocellular carcinoma tissues relative to adjacent non-tumorous tissues in the liver of human HCC patients. In addition, the present inventors have determined that PLVAP protein is mainly expressed in, and localizes to, vascular endothelial cells surrounding or within HCC tumors, but is not expressed in, or localized to, cells associated with other liver pathologies.

Accordingly, PLVAP represents a novel target for the diagnosis and treatment of HCC.

Methods of Therapy

In one aspect, the invention relates to a method of treating hepatocellular carcinoma (HCC) in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of at least one PLVAP antagonist, wherein the PLVAP antagonist inhibits formation, growth, vascularization and/or progression of one or more HCC tumors in the liver of the subject. In a particular aspect, a PLVAP antagonist of the invention inhibits the expression or activity of PLVAP protein in vascular endothelial cells surrounding hepatocytes in the liver of HCC patients.

In one aspect, a therapeutically-effective amount of a PLVAP antagonist is administered to a subject in need thereof to inhibit tumor growth or kill tumor cells. For example, agents which directly inhibit tumor growth (e.g., chemotherapeutic agents) are conventionally administered at a particular dosing schedule and level to achieve the most effective therapy (e.g., to best kill tumor cells). Generally, about the maximum tolerated dose is administered during a relatively short treatment period (e.g., one to several days), which is followed by an off-therapy period. In a particular example, the chemotherapeutic cyclophosphamide is administered at a maximum tolerated dose of 150 mg/kg every other day for three doses, with a second cycle given 21 days after the first cycle. (Browder et al. Can Res 60:1878-1886, 2000).

An therapeutically-effective amount of PLVAP antagonist (e.g., inhibitory small molecules, neutralizing antibodies, inhibitory nucleic acids (e.g., siRNA, antisense nucleotides)) can be administered, for example, in a first cycle in which about the maximum tolerated dose of the antagonist is administered in one interval/dose, or in several closely spaced intervals (minutes, hours, days) with another/second cycle administered after a suitable off-therapy period (e.g., one or more weeks). Suitable dosing schedules and amounts for a PLVAP antagonist can be readily determined by a clinician of ordinary skill. Decreased toxicity of a particular PLVAP antagonist as compared to chemotherapeutic agents can allow for the time between administration cycles to be shorter. When used as an adjuvant therapy (to, e.g., surgery, radiation therapy, other primary therapies), a therapeutically-effective amount of a PLVAP antagonist is preferably administered on a dosing schedule that is similar to that of the other cancer therapy (e.g., chemotherapeutics), or on a dosing schedule determined by the skilled clinician to be more/most effective at inhibiting (reducing, preventing) tumor growth. A treatment regimen for a therapeutically-effective amount of an antibody PLVAP antagonist can be, for example, from about 0.01 mg/kg to about 300 mg/kg body weight per treatment and preferably from about 0.01 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 10 mg/kg, from about 1 mg/kg to about 10 mg/kg every 1 to 7 days over a period of about 4 to about 6 months. A treatment regimen for an anti-tumor effective amount of a small molecule PLVAP antagonist can be, for example, from about 0.001 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 10 mg/kg, from about 0.01 mg/kg to about 1 mg/kg, every 1 to 7 days over a period of about 4 to about 6 months.

In another aspect, a PLVAP antagonist can be administered in a metronomic dosing regime, whereby a lower dose is administered more frequently relative to maximum tolerated dosing. A number of preclinical studies have demonstrated superior anti-tumor efficacy, potent antiangiogenic effects, and reduced toxicity and side effects (e.g., myelosuppression) of metronomic regimes compared to maximum tolerated dose (MTD) counterparts (Bocci, et al., Cancer Res, 62:6938-6943, (2002); Bocci, et al., Proc. Natl. Acad. Sci., 100(22):12917-12922, (2003); and Bertolini, et al., Cancer Res, 63(15):4342-4346, (2003)). Metronomic chemotherapy appears to be effective in overcoming some of the shortcomings associated with chemotherapy.

A PLVAP antagonist can be administered in a metronomic dosing regime to inhibit (reduce, prevent) angiogenesis in a patient in need thereof as part of an anti-angiogenic therapy. Such anti-angiogenic therapy may indirectly affect (inhibit, reduce) tumor growth by blocking the formation of new blood vessels that supply tumors with nutrients needed to sustain tumor growth and enable tumors to metastasize. Starving the tumor of nutrients and blood supply in this manner can eventually cause the cells of the tumor to die by necrosis and/or apoptosis. Previous work has indicated that the clinical outcomes (inhibition of endothelial cell-mediated tumor angiogenesis and tumor growth) of cancer therapies that involve the blocking of angiogenic factors (e.g., VEGF, bFGF, TGF-α, IL-8, PDGF) or their signaling have been more efficacious when lower dosage levels are administered more frequently, providing a continuous blood level of the antiangiogenic agent. (See Browder et al. Can. Res. 60:1878-1886, 2000; Folkman J., Sem. Can. Biol. 13:159-167, 2003). An anti-angiogenic treatment regimen has been used with a targeted inhibitor of angiogenesis (thrombospondin 1 and platelet growth factor-4 (TNP-470)) and the chemotherapeutic agent cyclophosphamide. Every 6 days, TNP-470 was administered at a dose lower than the maximum tolerated dose and cyclophosphamide was administered at a dose of 170 mg/kg. Id. This treatment regimen resulted in complete regression of the tumors. Id. In fact, anti-angiogenic treatments are most effective when administered in concert with other anti-cancer therapeutic agents, for example, those agents that directly inhibit tumor growth (e.g., chemotherapeutic agents). Id.

The therapeutic methods described herein comprise administering a PLVAP antagonist to a subject. The PLVAP antagonist may be administered to the individual in need thereof as a primary therapy (e.g., as the principal therapeutic agent in a therapy or treatment regimen); as an adjunct therapy (e.g., as a therapeutic agent used together with another therapeutic agent in a therapy or treatment regime, wherein the combination of therapeutic agents provides the desired treatment; “adjunct therapy” is also referred to as “adjunctive therapy”); in combination with an adjunct therapy; as an adjuvant therapy (e.g., as a therapeutic agent that is given to the subject in need thereof after the principal therapeutic agent in a therapy or treatment regimen has been given); or in combination with an adjuvant therapy (e.g., chemotherapy (e.g., tamoxifen, cisplatin, mitomycin, 5-fluorouracil, doxorubicin, sorafenib, octreotide, dacarbazine (DTIC), Cis-platinum, cimetidine, cyclophophamide), radiation therapy (e.g., proton beam therapy), hormone therapy (e.g., anti-estrogen therapy, androgen deprivation therapy (ADT), luteinizing hormone-releasing hormone (LH-RH) agonists, aromatase inhibitors (AIs, such as anastrozole, exemestane, letrozole), estrogen receptor modulators (e.g., tamoxifen, raloxifene, toremifene)), or biological therapy). Numerous other therapies can also be administered during a cancer treatment regime to mitigate the effects of the disease and/or side effects of the cancer treatment including therapies to manage pain (narcotics, acupuncture), gastric discomfort (antacids), dizziness (anti-veritgo medications), nausea (anti-nausea medications), infection (e.g., medications to increase red/white blood cell counts) and the like, all of which are readily appreciated by the person skilled in the art.

Thus, a PLVAP antagonist can be administered as an adjuvant therapy (e.g., with another primary cancer therapy or treatment). As an adjuvant therapy, the PLVAP antagonist can be administered before, after or concurrently with a primary therapy like radiation and/or the surgical removal of a tumor(s). In some embodiments, the method comprises administering a therapeutically effective amount of a PLVAP antagonist and one or more other therapies (e.g., adjuvant therapies, other targeted therapies). An adjuvant therapy (e.g., a chemotherapeutic agent) and/or the one or more other targeted HCC therapies and the PLVAP antagonist can be co-administered simultaneously (e.g., concurrently) as either separate formulations or as a joint formulation. Alternatively, the therapies can be administered sequentially, as separate compositions, within an appropriate time frame (e.g., a cancer treatment session/interval such as 1.5 to 5 hours) as determined by the skilled clinician (e.g., a time sufficient to allow an overlap of the pharmaceutical effects of the therapies). The adjuvant therapy and/or one or more other targeted HCC therapies and the PLVAP antagonist can be administered in a single dose or multiple doses in an order and on a schedule suitable to achieve a desired therapeutic effect (e.g., inhibition of tumor growth, inhibition of angiogenesis, and/or inhibition of cancer metastasis).

One or more agents that are PLVAP antagonists can be administered in single or multiple doses. Suitable dosing and regimens of administration can be determined by a clinician and are dependent on the agent(s) chosen, pharmaceutical formulation and route of administration, various patient factors and other considerations. With respect to the administration of a PLVAP antagonist with one or more other therapies or treatments (adjuvant, targeted, cancer treatment-associated, and the like) the PLVAP antagonist is typically administered as a single dose (by e.g., injection, infusion, orally), followed by repeated doses at particular intervals (e.g., one or more hours) if desired or indicated.

The amount of the PLVAP antagonist to be administered (e.g., a therapeutically effective amount) can be determined by a clinician using the guidance provided herein and other methods known in the art and is dependent on several factors including, for example, the particular agent chosen, the subject's age, sensitivity, tolerance to drugs and overall well-being. For example, suitable dosages for a small molecule can be from about 0.001 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 10 mg/kg, from about 0.01 mg/kg to about 1 mg/kg body weight per treatment. Suitable dosages for antibodies can be from about 0.01 mg/kg to about 300 mg/kg body weight per treatment and preferably from about 0.01 mg/kg to about 100 mg/kg, from about 0.01 mg/kg to about 10 mg/kg, from about 1 mg/kg to about 10 mg/kg body weight per treatment. Where the PLVAP antagonist is a polypeptide (linear, cyclic, mimetic), the preferred dosage will result in a plasma concentration of the peptide from about 0.1 μg/mL to about 200 μg/mL. Determining the dosage for a particular agent, patient and cancer is well within the abilities of one of skill in the art. Preferably, the dosage does not cause or produces minimal adverse side effects (e.g., immunogenic response, nausea, dizziness, gastric upset, hyperviscosity syndromes, congestive heart failure, stroke, pulmonary edema).

Methods for Administration

According to the methods of the invention, a therapeutically effective amount of a PLVAP antagonist (e.g., antibody, such as an antibody labeled with a radioactive isotope) is administered to a mammalian subject to treat HCC.

A variety of routes of administration can be used including, for example, oral, dietary, topical, transdermal, rectal, parenteral (e.g., intraaterial, intravenous, intramuscular, subcutaneous injection, intradermal injection), intravenous infusion and inhalation (e.g., intrabronchial, intranasal or oral inhalation, intranasal drops) routes of administration, depending on the agent and the particular cancer to be treated. Administration can be local or systemic as indicated. The preferred mode of administration can vary depending on the particular agent chosen; however, intraarterial administration (e.g., hepatic arterial infusion, trans-arterial chemoembolization (TACE)) is generally preferred to administer therapeutic agents (e.g., antibodies, such as antibodies labeled with a radioactive isotope) of the invention to treat hepatocellular carcinoma.

For example, using hepatic arterial infusion, chemotherapeutic agents (e.g., PLVAP antibodies, such as PLVAP antibodies labeled with a radioactive isotope) can be delivered directly to an HCC tumor through the hepatic artery, for example, during routine TACE treatment of HCC (Camma, et al. Radiology 224:47-54, 2002; Befeler, et al. Clinics in Liver Disease 9:287-300, 2005; Abou-Alfa JAMA 299:1716-1718, 2008). This procedure is done with the help of fluoroscopy (type of x-ray) imaging. Briefly, a catheter is inserted into the femoral artery in the groin and is threaded into the aorta. From the aorta, the catheter is advanced into the hepatic artery or its branches. Once the branches of the hepatic artery that feed the liver cancer are identified, the chemotherapy is infused. An interventional radiologist, who usually carries out this procedure, can determine the amount of chemotherapy that a patient receives at each session. Some patients may undergo repeat sessions at 6 to 12 week intervals. Imaging studies of the liver are repeated in six to 12 weeks to assess the size of the tumor in response to the treatment.

Alternatively, trans-arterial chemoembolization (TACE), a procedure that is similar to intraarterial infusion, can be used to administer PLVAP antagonists, e.g., antibodies) to a subject in need thereof. In TACE, intraarterial infusion of a therapeutic agent is combined with the additional step of blocking (i.e., embolizing) the small blood vessels with particular blocking compounds, such as gelfoam, oil emulsion, or even small metal coils. Thus, TACE has the potential advantages of exposing the tumor to high concentrations of chemotherapy and confining the agents locally in order to prevent or reduce their being carried away by the blood stream. At the same time, TACE deprives the tumor of its needed blood supply, which can result in the damage or death of the tumor cells.

For intraarterial administration of PLVAP antibodies, it is preferred to use antibodies having high affinities to PLVAP (e.g., a K_(d) less than 10⁻⁷ M) so that the infused antibodies will be concentrated in blood vessels of HCC. Chimeric and humanized antibodies are expected to have circulatory half-lives of up to four and up to 14-21 days, respectively. In a particular embodiment, high affinity PLVAP antibodies (e.g., antigen binding fragments, single chain antibodies) with short circulatory half-lives (e.g., about 1 day to about 5 days, for example, about 1, 2, 3, 4 or 5 days) are administered to a patient in order to reduce any toxicity and other adverse side-effects resulting from their administration. In another embodiment, high affinity PLVAP antibodies with long circulatory half-lives (e.g., about 5 days to about 24 days) are administered to a patient to treat HCC.

In many cases it will be preferable to administer a large loading dose followed by periodic (e.g., weekly) maintenance doses over the treatment period. Antibodies can also be delivered by slow-release delivery systems, pumps, and other known delivery systems for continuous infusion into HCC. Dosing regimens may be varied to provide the desired circulating levels of a particular antibody based on its pharmacokinetics. Thus, doses will be calculated so that the desired therapeutic level is maintained.

The actual dose and treatment regimen will be determined by the physician, taking into account the nature of the cancer (primary or metastatic), number and size of tumors, other therapies, and patient characteristics. In view of the life-threatening nature of hepatocellular carcinoma, large doses with significant side effects may be employed.

Nucleic acid-based PLVAP antagonists (e.g., siRNAs, antisense oligonucleotides, natural or synthetic nucleic acids, nucleic acid analogs) can be introduced into a mammalian subject of interest in a number of ways. For instance, nucleic acids may be expressed endogenously from expression vectors or PCR products in host cells or packaged into synthetic or engineered compositions (e.g., liposomes, polymers, nanoparticles) that can then be introduced directly into the bloodstream of a mammalian subject (by, e.g., injection, infusion). Anti-PLVAP nucleic acids or nucleic acid expression vectors (e.g., retroviral, adenoviral, adeno-associated and herpes simplex viral vectors, engineered vectors, non-viral-mediated vectors) can also be introduced into a mammalian subject directly using established gene therapy strategies and protocols (see e.g., Tochilin V. P. Annu Rev Biomed Eng 8:343-375, 2006; Recombinant DNA and Gene Transfer, Office of Biotechnology Activities, National Institutes of Health Guidelines).

Similarly, where the agent is a protein or polypeptide, the agent can be administered via in vivo expression of recombinant protein. In vivo expression can be accomplished by somatic cell expression according to suitable methods (see, e.g., U.S. Pat. No. 5,399,346). Further, a nucleic acid encoding the polypeptide can also be incorporated into retroviral, adenoviral or other suitable vectors (preferably, a replication deficient infectious vector) for delivery, or can be introduced into a transfected or transformed host cell capable of expressing the polypeptide for delivery. In the latter embodiment, the cells can be implanted (alone or in a barrier device), injected or otherwise introduced in an amount effective to express the polypeptide in a therapeutically effective amount.

Diagnostic and Prognostic Methods

The present invention encompasses diagnostic and prognostic methods that comprise assessing expression of PLVAP in a sample (e.g., liver biopsy, fine needle aspiration sample) from a mammalian subject (e.g., a mammalian subject who has a liver tumor). For diagnostic methods of the invention, expression of PLVAP in the sample, or increased expression of PLVAP in the sample relative to a suitable control, indicates that the subject has HCC, and/or that the subject is a candidate for an anti-cancer therapy using a PLVAP antagonist.

For prognostic methods of the invention, expression of PLVAP in a sample from a subject, or increased expression of PLVAP in the sample relative to a suitable control, indicates a poor prognosis. The prognosis can be a prognosis for patient survival, a prognosis for risk of metastases and/or a prognosis for risk of relapse.

Suitable samples for these methods include a tissue sample, a biological fluid sample, a cell(s) (e.g., a tumor cell) sample, and the like. Any means of sampling from a subject, for example, by blood draw, spinal tap, tissue smear or scrape, or tissue biopsy can be used to obtain a sample. Thus, the sample can be a biopsy specimen (e.g., tumor, polyp, mass (solid, cell)), aspirate, smear or blood sample. The sample can be a tissue from a liver that has a tumor (e.g., cancerous growth) and/or tumor cells, or is suspected of having a tumor and/or tumor cells. For example, a tumor biopsy can be obtained in an open biopsy, a procedure in which an entire (excisional biopsy) or partial (incisional biopsy) mass is removed from a target area. Alternatively, a tumor sample can be obtained through a percutaneous biopsy, a procedure performed with a needle-like instrument through a small incision or puncture (with or without the aid of a imaging device) to obtain individual cells or clusters of cells (e.g., a fine needle aspiration (FNA)) or a core or fragment of tissues (core biopsy). The biopsy samples can be examined cytologically (e.g., smear), histologically (e.g., frozen or paraffin section) or using any other suitable method (e.g., molecular diagnostic methods). A tumor sample can also be obtained by in vitro harvest of cultured human cells derived from an individual's tissue. Tumor samples can, if desired, be stored before analysis by suitable storage means that preserve a sample's protein and/or nucleic acid in an analyzable condition, such as quick freezing, or a controlled freezing regime. If desired, freezing can be performed in the presence of a cryoprotectant, for example, dimethyl sulfoxide (DMSO), glycerol, or propanediol-sucrose. Tumor samples can be pooled, as appropriate, before or after storage for purposes of analysis. The tumor sample can be from a patient who has a liver cancer, for example, hepatocellular carcinoma.

Suitable assays that can be used to assess the presence or amount of a PLVAP in a sample (e.g., biological sample) are known to those of skill in the art. Methods to detect a PLVAP protein or peptide include immunological and immunochemical methods like flow cytometry (e.g., FACS analysis), enzyme-linked immunosorbent assays (ELISA), including chemiluminescence assays, radioimmunoassay, immunoblot (e.g., Western blot), immunohistochemistry (IHC), and other antibody-based quantitative methods (e.g., Luminex® beads-based assays). Other suitable methods include, for example, mass spectroscopy. For example, antibodies to PLVAP can be used to determine the presence and/or expression level of PLVAP in a sample directly or indirectly using, e.g., immunohistochemistry (IHC). For instance, paraffin sections can be taken from a biopsy, fixed to a slide and combined with one or more antibodies by suitable methods. In a particular embodiment, detection of PLVAP protein in vascular endothelial cells surrounding hepatocytes in a sample is indicative of HCC.

An exemplary ELISA assay for use in diagnostic and prognostic applications of the invention is described in Example 9 herein.

Methods to detect PLVAP gene expression include PLVAP nucleic acid amplification and/or visualization. To detect PLVAP gene expression, a nucleic acid can be isolated from an individual by suitable methods which are routine in the art (see, e.g., Sambrook et al., 1989). Isolated nucleic acid can then be amplified (by e.g., polymerase chain reaction (PCR) (e.g., direct PCR, quantitative real time PCR, reverse transcriptase PCR), ligase chain reaction, self sustained sequence replication, transcriptional amplification system, Q-Beta Replicase, or the like) and visualized (by e.g., labeling of the nucleic acid during amplification, exposure to intercalating compounds/dyes, probes). PLVAP RNA (e.g., mRNA) or expression thereof can also be detected using a nucleic acid probe, for example, a labeled nucleic acid probe (e.g., fluorescence in situ hybridization (FISH)) directly in a paraffin section of a tissue sample taken from, e.g., a tumor biopsy, or using other suitable methods. PLVAP gene expression thereof can also be assessed by Southern blot or in solution (e.g., dyes, probes). Further, a gene chip, microarray, probe (e.g., quantum dots) or other such device (e.g., sensor, nanonsensor/detector) can be used to detect expression and/or differential expression of a PLVAP gene.

In one embodiment, a hepatocellular carcinoma can be diagnosed by detecting expression of a PLVAP gene product (e.g., PLVAP mRNA, PLVAP protein) in a sample from a patient. Thus, the method does not require that PLVAP expression in the sample from the patient be compared to the expression of PLVAP in a control. The presence or absence of PLVAP can be ascertained by the methods described herein or other suitable assays. In another embodiment, an increase in expression of PLVAP can be determined by comparison of PLVAP expression in the sample to that of a suitable control. Suitable controls include, for instance, a non-neoplastic tissue sample from the individual, non-cancerous cells, non-metastatic cancer cells, non-malignant (benign) cells or the like, or a suitable known or determined reference standard. The reference standard can be a typical, normal or normalized range or level of expression of a PLVAP protein or RNA (e.g., an expression standard). Thus, the method does not require that expression of the gene/protein be assessed in a suitable control.

In another embodiment, a hepatocellular carcinoma can be diagnosed by detecting the PLVAP gene copy number in a sample from a patient. For example, in some embodiments, a PLVAP gene copy number that is greater than two (e.g., a gene copy number of 3 or 4) can be diagnostic of HCC. Typically, a normal human cell will have a PLVAP gene copy number of two. Therefore, a method of diagnosis based on PLVAP gene copy number does not require detecting the PLVAP gene copy number in a control sample from the patient, although a control may be used. Suitable controls include, for instance, a non-neoplastic tissue sample from the individual, non-cancerous cells, non-metastatic cancer cells, non-malignant (benign) cells or the like, or a suitable known or determined reference standard (e.g., a PLVAP gene copy number of two). The copy number of the PLVAP gene in a sample from a patient can be ascertained by suitable techniques, such as, for example, fluorescence in situ hybridization (FISH).

PLVAP Antibodies

As described herein, antibodies that bind PLVAP have utility in the diagnosis and treatment of HCC in human subjects. For example, antibodies that specifically bind PLVAP can be used to detect the presence of PLVAP on capillary endothelial cells of hepatocellular carcinoma in specimens of liver core biopsies or needle aspirates by immunohistochemical staining (IHC). In addition, antibodies (e.g., humanized antibodies, chimeric antibodies) to PLVAP can be labeled with a proper tracer (e.g., radioisotope) for immuno-positron emission tomography (immuno-PET) (Clin Cancer Res 12:1958-1960, 2006; Clin Cancer Res 12:2133-2140, 2006) to determine whether a space occupying lesion(s) in the liver of a subject is hepatocellular carcinoma. Anti-PLVAP antibodies (e.g., humanized antibodies) can also be labeled with a cytotoxic agent (radioactive or non-radioactive) for therapeutic purposes (Weiner L M, Adams G P, Von Mehren M. Therapeutic monoclonal antibodies: General principles. In: Cancer: Principles & Practice of Oncology. 6^(th) ed. DeVita V T, Hellman S, Rosenberg S A, eds. Philadelphia: Lippincott Williams & Wilkins; 2001:495-508; Levinson W, Jawetz E. Medical Microbiology & Immunology. 4^(th) ed. Stamford: Appleton & Lange; 1996:307-47; Scheinberg D A, Sgouros G, Junghans R P. Antibody-based immunotherapies for cancer. In: Cancer Chemotherapy & Biotherapy: Principles and Practice. 3^(rd) ed. Chabner B A, Longo D L, eds. Philadelphia: Lippincott Williams & Wilkins; 2001:850-82).

Accordingly, in one embodiment, the invention provides an antibody that binds (e.g., specifically binds) a PLVAP protein (e.g., a human PLVAP protein (SEQ ID NO:23)). Antibodies that specifically bind to a PLVAP protein can be polyclonal, monoclonal, human, chimeric, humanized, primatized, veneered, and single chain antibodies, as well as fragments of antibodies (e.g., Fv, Fc, Fd, Fab, Fab′, F(ab′), scFv, scFab, dAb), among others. (See e.g., Harlow et al., Antibodies A Laboratory Manual, Cold Spring Harbor Laboratory, 1988). Antibodies that specifically bind to a PLVAP protein can be produced, constructed, engineered and/or isolated by conventional methods or other suitable techniques. For example, antibodies which are specific for a PLVAP protein can be raised against an appropriate immunogen, such as a recombinant mammalian (e.g., human) PLVAP protein (e.g., SEQ ID NO:23) or a portion thereof (e.g., SEQ ID NO:2, SEQ ID NO:38, SEQ ID NO:40) (including synthetic molecules, e.g., synthetic peptides). A variety of such immunization methods have been described (see e.g., Kohler et al., Nature, 256: 495-497 (1975) and Eur. J. Immunol. 6: 511-519 (1976); Milstein et al., Nature 266: 550-552 (1977); Koprowski et al., U.S. Pat. No. 4,172,124; Harlow, E. and D. Lane, 1988, Antibodies: A Laboratory Manual, (Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y.); Current Protocols In Molecular Biology, Vol. 2 (Supplement 27, Summer '94), Ausubel, F. M. et al., Eds., (John Wiley & Sons: New York, N.Y.), Chapter 11, (1991)). Antibodies can also be raised by immunizing a suitable host (e.g., mouse) with cells that express PLVAP (e.g., cancer cells/cell lines) or cells engineered to express PLVAP (e.g., transfected cells). (See e.g., Chuntharapai et al., J. Immunol., 152:1783-1789 (1994); Chuntharapai et al. U.S. Pat. No. 5,440,021).

At an appropriate time after immunization, e.g., when the antibody titers are highest, antibody-producing cells can be obtained from the immunized animal and used to prepare monoclonal antibodies by standard techniques, such as the hybridoma technique originally described by Kohler and Milstein (Nature 256:495-497, 1975), the human B cell hybridoma technique (Kozbor et al., Immunol. Today 4:72, 1983), the EBV-hybridoma technique (Cole et al., Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96, 1985) or trioma techniques. The technology for producing hybridomas is well known (see generally Current Protocols in Immunology, Coligan et al., (eds.) John Wiley & Sons, Inc., New York, N.Y., 1994). Briefly, an immortal cell line (typically a myeloma) is fused to lymphocytes (typically splenocytes) from a mammal immunized with an immunogen as described above, and the culture supernatants of the resulting hybridoma cells are screened to identify a hybridoma producing a monoclonal antibody that binds a polypeptide described herein.

Any of the many well known protocols used for fusing lymphocytes and immortalized cell lines can be applied for the purpose of generating a monoclonal antibody to a polypeptide of the invention (see, e.g., Current Protocols in Immunology, supra; Galfre et al., Nature, 266:55052, 1977; R. H. Kenneth, in Monoclonal Antibodies: A New Dimension In Biological Analyses, Plenum Publishing Corp., New York, N.Y., 1980; and Lerner, Yale J. Biol. Med. 54:387-402, 1981). Moreover, the ordinarily skilled worker will appreciate that there are many variations of such methods that also would be useful.

In one embodiment, the invention relates to a monoclonal anti-PLVAP antibody produced by murine hybridoma KFCC-GY4 (ATCC Patent Deposit Designation PTA-9963), having been deposited on Apr. 8, 2009 at the American Type Culture Collection (ATCC), P.O. Box 1549, Manassas, Va. 20108, United States of America. In another embodiment, the invention relates to a monoclonal anti-PLVAP antibody produced by murine hybridoma KFCC-GY5 (ATCC Patent Deposit Designation PTA-9964), having been deposited on Apr. 8, 2009 at the American Type Culture Collection (ATCC), P.O. Box 1549, Manassas, Va. 20108, United States of America. The invention further relates to the murine hybridoma cell lines KFCC-GY4 (ATCC Patent Deposit Designation PTA-9963) and KFCC-GY5 (ATCC Patent Deposit Designation PTA-9964), themselves, as well as cells obtained from these hybridomas.

In one alternative to preparing monoclonal antibody-secreting hybridomas, a monoclonal antibody to a PLVAP protein can be identified and isolated by screening a recombinant combinatorial immunoglobulin library (e.g., an antibody phage display library) with the target polypeptide to thereby isolate immunoglobulin library members that bind the polypeptide. Kits for generating and screening phage display libraries are commercially available (e.g., the Pharmacia Recombinant Phage Antibody System, Catalog No. 27-9400-01; and the Stratagene SurfZAP™ Phage Display Kit, Catalog No. 240612). Additionally, examples of methods and reagents particularly amenable for use in generating and screening antibody display libraries can be found in, for example, U.S. Pat. No. 5,223,409; PCT Publication No. WO 92/18619; PCT Publication No. WO 91/17271; PCT Publication No. WO 92/20791; PCT Publication No. WO 92/15679; PCT Publication No. WO 93/01288; PCT Publication No. WO 92/01047; PCT Publication No. WO 92/09690; PCT Publication No. WO 90/02809; Fuchs et al., Bio/Technology 9:1370-1372, 1991; Hay et al., Hum. Antibodies Hybridomas 3:81-85, 1992; Huse et al., Science 246:1275-1281, 1989; and Griffiths et al., EMBO J. 12:725-734, 1993.

Antibody fragments (e.g., antigen-binding fragments) can be produced by enzymatic cleavage or by recombinant techniques. For example, papain or pepsin cleavage can generate Fab or F(ab′)₂ fragments, respectively. Other proteases with the requisite substrate specificity can also be used to generate Fab or F(ab′)₂ fragments.

Antibodies can also be produced in a variety of truncated forms using antibody genes in which one or more stop codons has been introduced upstream of the natural stop site. For example, a chimeric gene encoding a F(ab′)₂ heavy chain portion can be designed to include DNA sequences encoding the CH₁ domain and hinge region of the heavy chain.

Single chain, human, chimeric, humanized, primatized (CDR-grafted), or veneered antibodies comprising portions derived from different species, are also encompassed by the present invention and the term “antibody”. The various portions of these antibodies can be joined together chemically by conventional techniques, or can be prepared as a contiguous protein using genetic engineering techniques. For example, nucleic acids encoding a chimeric or humanized chain can be expressed to produce a contiguous protein. See, e.g., Cabilly et al., U.S. Pat. No. 4,816,567; Cabilly et al., European Patent No. 0,125,023 B1; Boss et al., U.S. Pat. No. 4,816,397; Boss et al., European Patent No. 0,120,694 B1; Neuberger, M. S. et al., WO 86/01533; Neuberger, M. S. et al., European Patent No. 0,194,276 B1; Winter, U.S. Pat. No. 5,225,539; Winter, European Patent No. 0,239,400 B1; Queen et al., European Patent No. 0 451 216 B1; and Padlan, E. A. et al., EP 0 519 596 A1. See also, Newman, R. et al., BioTechnology, 10: 1455-1460 (1992), regarding primatized antibody, and Ladner et al., U.S. Pat. No. 4,946,778 and Bird, R. E. et al., Science, 242: 423-426 (1988)) regarding single chain antibodies.

In a particular embodiment, the invention relates to chimeric antibodies that specifically bind to PLVAP (e.g., a human PLVAP protein comprising SEQ ID NO:23). In one embodiment, chimeric antibody of the invention comprises at least one heavy chain and at least one light chain (e.g., kappa light chain) of human IgG4. The production and characterization of exemplary chimeric antibodies of the invention are described in Example 7 herein.

In another embodiment, the invention relates to humanized antibodies that specifically bind to PLVAP (e.g., a human PLVAP protein comprising SEQ ID NO:23). Humanized antibodies of the invention can comprise, for example, at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:74, SEQ ID NO:76, SEQ ID NO:78, SEQ ID NO:80, SEQ ID NO:82, SEQ ID NO:84, SEQ ID NO:86, SEQ ID NO:66, SEQ ID NO:68, SEQ ID NO:94, SEQ ID NO:96, SEQ ID NO:98, SEQ ID NO:100, SEQ ID NO:102 and a combination thereof and/or at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:70, SEQ ID NO:72, SEQ ID NO:88, SEQ ID NO:90, SEQ ID NO:92, SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO:64, SEQ ID NO:104, SEQ ID NO:106, SEQ ID NO:108 and a combination thereof.

Humanized antibodies can be produced using synthetic or recombinant DNA technology using standard methods or other suitable techniques. Nucleic acid (e.g., cDNA) sequences coding for humanized variable regions can also be constructed using PCR mutagenesis methods to alter DNA sequences encoding a human or humanized chain, such as a DNA template from a previously humanized variable region (see e.g., Kamman, M., et al., Nucl. Acids Res., 17: 5404 (1989)); Sato, K., et al., Cancer Research, 53: 851-856 (1993); Daugherty, B. L. et al., Nucleic Acids Res., 19(9): 2471-2476 (1991); and Lewis, A. P. and J. S. Crowe, Gene, 101: 297-302 (1991)). Using these or other suitable methods, variants can also be readily produced. In one embodiment, cloned variable regions (e.g., dAbs) can be mutated, and sequences encoding variants with the desired specificity can be selected (e.g., from a phage library; see e.g., Krebber et al., U.S. Pat. No. 5,514,548; Hoogenboom et al., WO 93/06213, published Apr. 1, 1993).

Humanized antibodies can also be produced by and/or obtained from commercial sources including, for example, Antitope Limited (Cambridge, UK). An exemplary method of producing humanized antibodies, which is based on the Composite Human Antibody™ technology of Antitope Limited, is described in Example 8 herein.

Other suitable methods of producing or isolating antibodies of the requisite specificity can be used, including, for example, methods which select a recombinant antibody or antibody-binding fragment (e.g., dAbs) from a library (e.g., a phage display library), or which rely upon immunization of transgenic animals (e.g., mice). Transgenic animals capable of producing a repertoire of human antibodies are well-known in the art (e.g., Xenomouse® (Abgenix, Fremont, Calif.)) and can be produced using suitable methods (see e.g., Jakobovits et al., Proc. Natl. Acad. Sci. USA, 90: 2551-2555 (1993); Jakobovits et al., Nature, 362: 255-258 (1993); Lonberg et al., U.S. Pat. No. 5,545,806; Surani et al., U.S. Pat. No. 5,545,807; Lonberg et al., WO 97/13852).

Once produced, an antibody specific for PLVAP can be readily identified using methods for screening and isolating specific antibodies that are well known in the art. See, for example, Paul (ed.), Fundamental Immunology, Raven Press, 1993; Getzoff et al., Adv. in Immunol. 43:1-98, 1988; Goding (ed.), Monoclonal Antibodies: Principles and Practice, Academic Press Ltd., 1996; Benjamin et al., Ann. Rev. Immunol. 2:67-101, 1984. A variety of assays can be utilized to detect antibodies that specifically bind to PLVAP proteins. Exemplary assays are described in detail in Antibodies: A Laboratory Manual, Harlow and Lane (Eds.), Cold Spring Harbor Laboratory Press, 1988. Representative examples of such assays include: concurrent immunoelectrophoresis, radioimmunoassay, radioimmuno-precipitation, enzyme-linked immunosorbent assay (ELISA), dot blot or Western blot assays, inhibition or competition assays, and sandwich assays.

In certain embodiments, the antibodies of the invention have a high binding affinity for PLVAP. Such antibodies will preferably have an affinity (e.g., binding affinity) for PLVAP, expressed as K_(d), of at least about 10⁻⁷ M (e.g., about 0.4×10⁻⁷ M, about 0.6×10⁻⁷ M, about 4.06×10⁻⁷ M, about 4.64×10⁻⁷ M), or higher, for example, at least about 10⁻⁸ M (e.g., about 5.98×10⁻⁸ M), at least about 10⁻⁹ M, or at least about 10⁻¹⁰ M (e.g., about 9.78×10⁻¹⁰ M), such as about 9.78×10⁻¹⁰ M. The binding affinity of an antibody can be readily determined by one of ordinary skill in the art, for example, by Scatchard analysis (Scatchard, G., Ann. NY Acad. Sci. 51: 660-672, 1949). Binding affinity can also be determined using a commercially available biosensor instrument (BIACORE, Pharmacia Biosensor, Piscataway, N.J.), wherein protein is immobilized onto the surface of a receptor chip. See, Karlsson, J. Immunol. Methods 145:229-240, 1991 and Cunningham and Wells, J. Mol. Biol. 234:554-563, 1993. This system allows the determination of on- and off-rates, from which binding affinity can be calculated, and assessment of stoichiometry of binding.

The antibodies of the present invention can include a label, such as, for example, a detectable label that permits detection of the antibody, and proteins bound by the antibody (e.g., PLVAP), in a biological sample. A detectable label is particularly suitable for diagnostic applications. For example, a PLVAP antibody can be labeled with a radioactive isotope (radioisotope), which can be detected by one of skill in the art using a gamma counter, a scintillation counter or by autoradiography or other suitable means. Isotopes which are useful for the purpose of the present invention include, but are not limited to: ³H, ¹²⁵I, ¹³¹I, ³²P, ³⁵S, ¹⁴C, ⁵¹Cr, ³⁶Cl, ⁵⁷Co, ⁵⁸CO, ⁵⁹Fe and ⁷⁵Se.

Antibodies of the invention can also be labeled with a fluorescent compound (e.g., dyes). When the fluorescently labeled antibody is exposed to light of the proper wave length, its presence can then be detected due to the fluorescence of the compound. Among the most commonly used fluorescent labels are fluorescein isothiocyanate, rhodamine, phycoerytherin, phycocyanin, allophycocyanin, o-phthaldehyde and fluorescamine. the antibodies of the invention can also be labeled using fluorescence emitting metals such as ¹⁵²Eu, or others of the lanthanide series. These metals can be attached to the antibody molecule using such metal chelating groups as diethylenetriaminepentaacetic acid (DTPA), tetraaza-cyclododecane-tetraacetic acid (DOTA) or ethylenediaminetetraacetic acid (EDTA).

The antibodies of the present invention also can be coupled to a chemiluminescent compound. Examples of useful chemiluminescent labeling compounds are luminol, isoluminol, theromatic acridinium ester, imidazole, acridinium salt and oxalate ester.

Likewise, a bioluminescent compound may be used to label the antibody of the present invention. Bioluminescence is a type of chemiluminescence found in biological systems in which a catalytic protein increases the efficiency of the chemiluminescent reaction. The presence of a bioluminescent protein is determined by detecting the presence of luminescence. Useful bioluminescent compounds for purposes of labeling antibodies are luciferin, luciferase and aequorin.

Detection of the labeled antibodies can be accomplished by a scintillation counter, for example, if the detectable label is a radioactive gamma emitter, or by a fluorometer, for example, if the label is a fluorescent material. In the case of an enzyme label, the detection can be accomplished by colorimetric methods which employ a substrate for the enzyme. Detection may also be accomplished by visual comparison of the extent of the enzymatic reaction of a substrate to similarly prepared standards.

Accordingly, the antibodies of the present invention can also be used as a stain for tissue sections. For example, a labeled antibody that binds to PLVAP can be contacted with a tissue sample, e.g., a liver tissue biopsy or fine needle aspirate from a patient. This section may then be washed and the label detected using an appropriate means.

For the purpose of treating HCC, PLVAP antibodies of the invention may include a radiolabel or other therapeutic agent that enhances destruction of cells expressing PLVAP (e.g., vascular endothelial cells surrounding HCC cells). Examples of suitable radioisotope labels for use in HCC therapy include, but are not limited to, ¹²⁵I, ¹³¹I, ⁹⁰Y, ⁶⁷Cu, ²¹⁷Bi, ²¹¹At, ²¹²Pb, ⁴⁷Sc, ¹⁰⁹Pd, ¹¹¹In and ¹¹⁸Re. Optionally, a label that emits α and β particles upon bombardment with neutron radiation, such as boron, can be used as a label for therapeutic PLVAP antibodies.

Therapeutic antibodies also may include a cytotoxic agent that is capable of selectively killing cells that express PLVAP. For example, bacterial toxins such as diphtheria toxin, or ricin can be used. Methods for producing antibodies comprising fragment A of diphtheria toxin are taught in U.S. Pat. No. 4,675,382 (1987). Diphtheria toxin contains two polypeptide chains. The B chain binds the toxin to a receptor on a cell surface. The A chain actually enters the cytoplasm and inhibits protein synthesis by inactivating elongation factor 2, the factor that translocates ribosomes along mRNA concomitant with hydrolysis of ETP. See Darnell, J. et al., in Molecular Cell Biology, Scientific American Books, Inc., page 662 (1986). Alternatively, an antibody comprising ricin, a toxic lectin, may be prepared. Other suitable cytotoxic agents are know by those of skill in the art.

For in vivo detection, PLVAP antibodies of the invention may be conjugated to radionuclides either directly or by using an intermediary functional group. An intermediary group which is often used to bind radioisotopes, which exist as metallic cations, to antibodies is diethylenetriaminepentaacetic acid (DTPA) or tetraaza-cyclododecane-tetraacetic acid (DOTA). Typical examples of metallic cations which are bound in this manner are ⁹⁹Tc, ¹²³I, ¹¹¹In, ¹³¹I, ⁹⁷Ru, ⁶⁷Cu, ⁶⁷Ga, and ⁶⁸Ga.

Moreover, the antibodies of the invention may be tagged with an NMR imaging agent which include paramagnetic atoms. The use of an NMR imaging agent allows the in vivo diagnosis of the presence of and the extent of HCC in a patient using NMR techniques. Elements which are particularly useful in this manner are ¹⁵⁷Gd, ⁵⁵Mn, ¹⁶²Dy, ⁵²Cr, and ⁵⁶ _(Fe.)

PLVAP Antagonists

A PLVAP antagonist of the invention can be any agent that inhibits (e.g., reduces, prevents) an activity of a PLVAP gene product. PLVAP activities include, but are not limited to, formation, growth, vascularization or progression of an HCC tumor. In a particular embodiment, a PLVAP antagonist inhibits an activity of a PLVAP gene product (e.g., PLVAP RNA, PLVAP protein) by specifically binding to the PLVAP gene product. PLVAP antagonists also encompass agents that inhibit (reduce, decrease, prevent) the expression (e.g., transcription, mRNA processing, translation) of a PLVAP gene or gene product (e.g., PLVAP RNA, PLVAP protein).

A PLVAP antagonist can be an antibody, a small molecule, a peptide, a peptidomimetic, or a nucleic acid, among others.

Antibody Antagonists

A PLVAP antagonist of the invention can be an antibody that specifically binds a PLVAP protein. Such antibodies include, but are not limited to, any of the PLVAP-specific antibodies described herein.

Small Molecule Antagonists

PLVAP antagonists can also be small molecules. Examples of small molecules include organic compounds, organometallic compounds, inorganic compounds, and salts of organic, organometallic or inorganic compounds. Atoms in a small molecule are typically linked together via covalent and/or ionic bonds. The arrangement of atoms in a small organic molecule may represent a chain (e.g. a carbon-carbon chain or a carbon-heteroatom chain), or may represent a ring containing carbon atoms, e.g. benzene or a policyclic system, or a combination of carbon and heteroatoms, i.e., heterocycles such as a pyrimidine or quinazoline. Although small molecules can have any molecular weight, they generally include molecules that are less than about 5,000 daltons. For example, such small molecules can be less than about 1000 daltons and, preferably, are less than about 750 daltons or, more preferably, are less than about 500 daltons. Small molecules and other non-peptidic PLVAP antagonists can be found in nature (e.g., identified, isolated, purified) and/or produced synthetically (e.g., by traditional organic synthesis, bio-mediated synthesis, or a combination thereof). See e.g. Ganesan, Drug Discov. Today 7(1): 47-55 (January 2002); Lou, Drug Discov. Today, 6(24): 1288-1294 (December 2001). Examples of naturally occurring small molecules include, but are not limited to, hormones, neurotransmitters, nucleotides, amino acids, sugars, lipids, and their derivatives.

Peptide Antagonists

The PLVAP antagonist of the invention can also be a peptide that binds to a PLVAP protein. The peptide can comprise any suitable L- and/or D-amino acid, for example, common α-amino acids (e.g., alanine, glycine, valine), non-α-amino acids (e.g., β-alanine, 4-aminobutyric acid, 6-aminocaproic acid, sarcosine, statine), and unusual amino acids (e.g., citrulline, homocitruline, homoserine, norleucine, norvaline, ornithine). The amino, carboxyl and/or other functional groups on a peptide can be free (e.g., unmodified) or protected with a suitable protecting group. Suitable protecting groups for amino and carboxyl groups, and methods for adding or removing protecting groups are known in the art and are disclosed in, for example, Green and Wuts, “Protecting Groups in Organic Synthesis”, John Wiley and Sons, 1991. The functional groups of a peptide can also be derivatized (e.g., alkylated) using art-known methods.

The peptide PLVAP antagonist can comprise one or more modifications (e.g., amino acid linkers, acylation, acetylation, amidation, methylation, terminal modifiers (e.g., cyclizing modifications)), if desired. The peptide can also contain chemical modifications (e.g., N-methyl-α-amino group substitution). In addition, the peptide antagonist can be an analog of a known and/or naturally-occurring peptide, for example, a peptide analog having conservative amino acid residue substitution(s). These modifications can improve various properties of the peptide (e.g., solubility, binding), including its PLVAP antagonist activity.

PLVAP antagonists that are peptides can be linear, branched or cyclic, e.g., a peptide having a heteroatom ring structure that includes several amide bonds. In a particular embodiment, the peptide is a cyclic peptide. Such peptides can be produced by one of skill in the art using standard techniques. For example, a peptide can be derived or removed from a native protein by enzymatic or chemical cleavage, or can be synthesized by suitable methods, for example, solid phase peptide synthesis (e.g., Merrifield-type synthesis) (see, e.g., Bodanszky et al. “Peptide Synthesis,” John Wiley & Sons, Second Edition, 1976). Peptides that are PLVAP antagonists can also be produced, for example, using recombinant DNA methodologies or other suitable methods (see, e.g., Sambrook J. and Russell D. W., Molecular Cloning: A Laboratory Manual, 3^(rd) Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 2001).

Peptides can be synthesized and assembled into libraries comprising a few to many discrete molecular species. Such libraries can be prepared using methods of combinatorial chemistry, and can be screened using any suitable method to determine if the library comprises peptides with a desired biological activity. Such peptide antagonists can then be isolated using suitable methods known by those of skill in the art.

Peptidomimetic Antagonists

PLVAP antagonists can also be peptidomimetics. For example, polysaccharides can be prepared that have the same functional groups as peptides. Peptidomimetics can be designed, for example, by establishing the three dimensional structure of a peptide agent in the environment in which it is bound or will bind to a target molecule. The peptidomimetic comprises at least two components, the binding moiety or moieties and the backbone or supporting structure.

The binding moieties are the chemical atoms or groups which will react or form a complex (e.g., through hydrophobic or ionic interactions) with a target molecule, for instance, human PLVAP. For example, the binding moieties in a peptidomimetic can be the same as those in a peptide or protein antagonist. The binding moieties can be an atom or chemical group which reacts with the receptor in the same or similar manner as the binding moiety in the peptide antagonist. For example, computational chemistry can be used to design peptide mimetics of peptides that bind PLVAP proteins. Examples of binding moieties suitable for use in designing a peptidomimetic for a basic amino acid in a peptide include nitrogen containing groups, such as amines, ammoniums, guanidines and amides or phosphoniums. Examples of binding moieties suitable for use in designing a peptidomimetic for an acidic amino acid include, for example, carboxyl, lower alkyl carboxylic acid ester, sulfonic acid, a lower alkyl sulfonic acid ester or a phosphorous acid or ester thereof.

The supporting structure is the chemical entity that, when bound to the binding moiety or moieties, provides the three dimensional configuration of the peptidomimetic. The supporting structure can be organic or inorganic. Examples of organic supporting structures include polysaccharides, polymers or oligomers of organic synthetic polymers (such as, polyvinyl alcohol or polylactide). It is preferred that the supporting structure possess substantially the same size and dimensions as the peptide backbone or supporting structure. This can be determined by calculating or measuring the size of the atoms and bonds of the peptide and peptidomimetic. In one embodiment, the nitrogen of the peptide bond can be substituted with oxygen or sulfur, for example, forming a polyester backbone. In another embodiment, the carbonyl can be substituted with a sulfonyl group or sulfinyl group, thereby forming a polyamide (e.g., a polysulfonamide). Reverse amides of the peptide can be made (e.g., substituting one or more-CONH-groups for a-NHCO-group). In yet another embodiment, the peptide backbone can be substituted with a polysilane backbone.

These compounds can be manufactured by known methods. For example, a polyester peptidomimetic can be prepared by substituting a hydroxyl group for the corresponding α-amino group on amino acids, thereby preparing a hydroxyacid and sequentially esterifying the hydroxyacids, optionally blocking the basic and acidic side chains to minimize side reactions. Determining an appropriate chemical synthesis route can generally be readily identified upon determining the chemical structure.

Peptidomimetics can be synthesized and assembled into libraries comprising a few to many discrete molecular species. Such libraries can be prepared using well-known methods of combinatorial chemistry, and can be screened to determine if the library comprises one or more peptidomimetics which have the desired activity. Such peptidomimetic antagonists can then be isolated by suitable methods.

Nucleic Acid Antagonists

PLVAP antagonists also include various nucleic acids, including nucleic acid molecules that inhibit PLVAP gene expression (e.g., siRNA, antisense oligonucleotides, ribozymes). For example, small interfering ribonucleic acids (siRNAs) and, similarly, short hairpin ribonucleic acids (shRNAs), which are processed into short siRNA-like molecules in a cell, can prevent the expression (translation) of the PLVAP protein. siRNA molecules can be polynucleotides that are generally about 20 to about 25 nucleotides long and are designed to bind a specific RNA sequence (e.g., a PLVAP mRNA sequence). siRNAs silence gene expression in a sequence-specific manner, binding to a target RNA (e.g., an RNA having the complementary sequence) and causing the RNA to be degraded by endoribonucleases. siRNA molecules able to inhibit the expression of the PLVAP gene product can be produced by suitable methods. There are several algorithms that can be used to design siRNA molecules that bind the sequence of a gene of interest (see e.g., Mateeva O. et al. Nucleic Acids Res. 35(8):Epub, 2007; Huesken D. et al., Nat. Biotechnol. 23:995-1001; Jagla B. et al., RNA 11:864-872, 2005; Shabalinea S. A. BMC Bioinformatics 7:65, 2005; Vert J. P. et al. BMC Bioinformatics 7:520, 2006). Expression vectors that can stably express siRNA or shRNA are available. (See e.g., Brummelkamp, T. R., Science 296: 550-553, 2002, Lee, N S, et al., Nature Biotechnol. 20:500-505, 2002; Miyagishi, M., and Taira, K. Nature Biotechnol. 20:497-500, 2002; Paddison, P. J., et al., Genes & Dev. 16:948-958, 2002; Paul, C. P., et al., Nature Biotechnol. 20:505-508; 2002; Sui, G., et al., Proc. Natl. Acad. Sci. USA 99(6):5515-5520, 2002; Yu, J-Y, et al., Proc. Natl. Acad. Sci. USA 99(9):6047-6052, 2002; Elbashir, S M, et al., Nature 411:494-498, 2001.). Stable expression of siRNA/shRNA molecules is advantageous in the treatment of cancer as it enables long-term expression of the molecules, potentially reducing and/or eliminating the need for repeated treatments.

Antisense oligonucleotides (e.g., DNA, riboprobes) can also be used as PLVAP antagonists to inhibit PLVAP expression. Antisense oligonucleotides are generally short (˜13 to ˜25 nucleotides) single-stranded nucleic acids which specifically hybridize to a target nucleic acid sequence (e.g., mRNA) and induce the degradation of the target nucleic acid (e.g., degradation of the RNA through RNase H-dependent mechanisms) or sterically hinder the progression of splicing or translational machinery. (See e.g., Dias N. and Stein C. A., Mol. Can. Ther. 1:347-355, 2002). There are a number of different types of antisense oligonucleotides that can be used as PLVAP antagonists including methylphosphonate oligonucleotides, phosphorothioate oligonucleotides, oligonucleotides having a hydrogen at the 2′-position of ribose replaced by an O-alkyl group (e.g., a methyl), polyamide nucleic acid (PNA), phosphorodiamidate morpholino oligomers (deoxyribose moiety is replaced by a morpholine ring), PN(N3′→P5′ replacement of the oxygen at the 3′ position on ribose by an amine group) and chimeric oligonucleotides (e.g., 2′-O-Methyl/phosphorothioate). Antisense oligonucleotides can be designed to be specific for a protein using predictive algorithms. (See e.g., Ding, Y., and Lawrence, C. E., Nucleic Acids Res., 29:1034-1046, 2001; Sczakiel, G., Front. Biosci., 5:D194-D201, 2000; Scherr, M., et al., Nucleic Acids Res., 28:2455-2461, 2000; Patzel, V., et al. Nucleic Acids Res., 27:4328-4334, 1999; Chiang, M. Y., et al., J. Biol. Chem., 266:18162-18171, 1991; Stull, R. A., et al., Nucleic Acids Res., 20:3501-3508, 1992; Ding, Y., and Lawrence, C. E., Comput. Chem., 23:387-400, 1999; Lloyd, B. H., et al., Nucleic Acids Res., 29:3664-3673, 2001; Mir, K. U., and Southern, E. M., Nat. Biotechnol., 17:788-792, 1999; Sohail, M., et al., Nucleic Acids Res., 29:2041-2051, 2001; Altman, R. K., et al., J. Comb. Chem., 1:493-508, 1999). The antisense oligonucleotides can be produced by suitable methods; for example, nucleic acid (e.g., DNA, RNA, PNA) synthesis using an automated nucleic acid synthesizer (from, e.g., Applied Biosystems) (see also Martin, P., Helv. Chim. Acta 78:486-504, 1995). Antisense oligonucleotides can also be stably expressed in a cell containing an appropriate expression vector.

Antisense oligonucleotides can be taken up by target cells (e.g., tumor cells) via the process of adsorptive endocytosis. Thus, in the treatment of a subject (e.g., mammalian), antisense PLVAP oligonucleotides can be delivered to target cells (e.g., tumor cells) by, for example, injection or infusion. For instance, purified oligonucleotides or siRNA/shRNA, can be administered alone or in a formulation with a suitable drug delivery vehicle (e.g., liposomes, cationic polymers, (e.g., poly-L-lysine, PAMAM dendrimers, polyalkylcyanoacrylate nanoparticles and polyethyleneimine) or coupled to a suitable carrier peptide (e.g., homeotic transcription factor, the Antennapedia peptide, Tat protein of HIV-1, E5CA peptide).

Ribozymes can also be used as PLVAP antagonists to inhibit PLVAP expression. Ribozymes are RNA molecules possessing enzymatic activity. One class of ribozymes is capable of repeatedly cleaving other separate RNA molecules into two or more pieces in a nucleotide base sequence specific manner. See Kim et al., Proc Natl Acad Sci USA, 84:8788 (1987); Haseloff & Gerlach, Nature, 334:585 (1988); and Jefferies et al., Nucleic Acid Res, 17:1371 (1989). Such ribozymes typically have two functional domains: a catalytic domain and a binding sequence that guides the binding of ribozymes to a target RNA through complementary base-pairing. Once a specifically-designed ribozyme is bound to a target mRNA, it enzymatically cleaves the target mRNA, typically reducing its stability and destroying its ability to directly translate an encoded protein. After a ribozyme has cleaved its RNA target, it is released from that target RNA and thereafter can bind and cleave another target. That is, a single ribozyme molecule can repeatedly bind and cleave new targets.

In accordance with the present invention, a ribozyme may target any portion of the mRNA encoding PLVAP. Methods for selecting a ribozyme target sequence and designing and making ribozymes are generally known in the art. See e.g., U.S. Pat. Nos. 4,987,071; 5,496,698; 5,525,468; 5,631,359; 5,646,020; 5,672,511; and 6,140,491, each of which is incorporated herein by reference in its entirety. For example, suitable ribozymes may be designed in various configurations such as hammerhead motifs, hairpin motifs, hepatitis delta virus motifs, group I intron motifs, or RNase P RNA motifs. See e.g., U.S. Pat. Nos. 4,987,071; 5,496,698; 5,525,468; 5,631,359; 5,646,020; 5,672,511; and 6,140,491; Rossi et al., AIDS Res Human Retroviruses 8:183 (1992); Hampel & Tritz, Biochemistry 28:4929 (1989); Hampel et al., Nucleic Acids Res, 18:299 (1990); Perrotta & Been, Biochemistry 31:16 (1992); and Guerrier-Takada et al., Cell, 35:849 (1983).

Ribozymes can be synthesized by the same methods used for normal RNA synthesis. For example, suitable methods are disclosed in Usman et al., J Am Chem Soc, 109:7845-7854 (1987) and Scaringe et al., Nucleic Acids Res, 18:5433-5441 (1990). Modified ribozymes may be synthesized by the methods disclosed in, e.g., U.S. Pat. No. 5,652,094; International Publication Nos. WO 91/03162; WO 92/07065 and WO 93/15187; European Patent Application No. 92110298.4; Perrault et al., Nature, 344:565 (1990); Pieken et al., Science, 253:314 (1991); and Usman & Cedergren, Trends Biochem Sci, 17:334 (1992).

PLVAP antagonists of the invention can also be nucleic acid molecules (e.g., oligonucleotides) that bind to, and inhibit the activity of, a PLVAP protein. Suitable nucleic acid PLVAP antagonists include aptamers, which are capable of binding to a particular molecule of interest (e.g., human PLVAP) with high affinity and specificity through interactions other than classic Watson-Crick base pairing (Tuerk and Gold, Science 249:505 (1990); Ellington and Szostak, Nature 346:818 (1990)).

Aptamers, like peptides generated by phage display or monoclonal antibodies (MAbs), are capable of specifically binding to selected targets and, through binding, block their targets' ability to function. Created by an in vitro selection process from pools of random sequence oligonucleotides, aptamers have been generated for over 100 proteins including growth factors, transcription factors, enzymes, immunoglobulins, and receptors. A typical aptamer is 10-15 kDa in size (30-45 nucleotides), binds its target with sub-nanomolar affinity, and discriminates against closely related targets (e.g., will typically not bind other proteins from the same gene family). A series of structural studies have shown that aptamers are capable of using the same types of binding interactions (hydrogen bonding, electrostatic complementarity, hydrophobic contacts, steric exclusion, etc.) that drive affinity and specificity in antibody-antigen complexes.

An aptamer that binds to a target of interest (e.g., a human PLVAP protein) can be generated and identified using a standard process known as “Systematic Evolution of Ligands by Exponential Enrichment” (SELEX), described in, e.g., U.S. Pat. No. 5,475,096 and U.S. Pat. No. 5,270,163.

Identification of PLVAP Antagonists

Agents having binding specificity for PLVAP gene products can be identified in a screen, for example, a high-throughput screen of chemical compounds and/or libraries (e.g., chemical, peptide, nucleic acid libraries).

Antibodies that specifically bind human PLVAP can be identified, for example, by screening commercially available combinatorial antibody libraries (Dyax Corp., MorphoSys AG). Suitable combinatorial antibody libraries and standard methods of screening these libraries are described in Hoet et al., Nature Biotechnology 23(3):344-348 (2005) and Rauchenberger et al., J. Biol. Chem. 278(40):38194-38205 (2003), the contents of which are incorporated herein by reference. Such libraries or collections of molecules can also be prepared using well-known chemical methods.

Alternatively murine antibodies that specifically bind human PLVAP can be identified, for example, by immunizing mice with PLVAP proteins, protein fragments or peptides, along with an adjuvant to break tolerance to the antigen. These antibodies can be screened for the desired specificity and activity and then humanized using known techniques to create suitable agents for the treatment of human disease.

Compounds or small molecules can be identified from numerous available libraries of chemical compounds from, for example, the Chemical Repository of the National Cancer Institute and the Molecular Libraries Small Molecules Repository (PubChem), as well as libraries of the Institute of Chemistry and Cell Biology at Harvard University and other libraries that are available from commercial sources (e.g., Chembridge, Peakdale, CEREP, MayBridge, Bionet). Such libraries or collections of molecules can also be prepared using well-known chemical methods, such as well-known methods of combinatorial chemistry. The libraries can be screened to identify compounds that bind and inhibit PLVAP.

Identified compounds can serve as lead compounds for further diversification using well-known methods of medicinal chemistry. For example, a collection of compounds that are structural variants of the lead can be prepared and screened for PLVAP binding and/or inhibitory activity. This can result in the development of a structure activity relationship that links the structure of the compounds to biological activity. Compounds that have suitable binding and inhibitory activity can be developed further for in vivo use.

Agents that bind PLVAP can be evaluated further for PLVAP antagonist activity. For example, a composition comprising a PLVAP protein can be used in a screen or binding assay to detect and/or identify agents that bind and antagonize the PLVAP protein. Compositions suitable for use include, for example, cells that naturally express a PLVAP protein (e.g., liver vascular endothelial cells), extracts of such cells, and recombinant PLVAP protein.

An agent that binds a PLVAP protein can be identified in a competitive binding assay, for example, in which the ability of a test agent to inhibit the binding of PLVAP to a reference agent is assessed. The reference agent can be a full-length PLVAP protein or a portion thereof. The reference agent can be labeled with a suitable label (e.g., radioisotope, epitope label, affinity label (e.g., biotin and avidin or streptavadin), spin label, enzyme, fluorescent group, chemiluminescent group, dye, metal (e.g., gold, silver), magnetic bead) and the amount of labeled reference agent required to saturate the PLVAP protein in the assay can be determined. The specificity of the formation of the complex between the PLVAP protein and the test agent can be determined using a suitable control (e.g., unlabeled agent, label alone).

The capacity of a test agent to inhibit formation of a complex between the reference agent and a PLVAP protein can be determined as the concentration of test agent required for 50% inhibition (IC₅₀ value) of specific binding of labeled reference agent. Specific binding is preferably defined as the total binding (e.g., total label in complex) minus the non-specific binding. Non-specific binding is preferably defined as the amount of label still detected in complexes formed in the presence of excess unlabeled reference agent. Reference agents suitable for use in the method include molecules and compounds which specifically bind to PLVAP, e.g., an antibody that binds PLVAP.

An agent that antagonizes a PLVAP protein can be identified by screening for agents that have an ability to antagonize (reduce, prevent, inhibit) one or more activities of PLVAP, such as, for example, tumor vascularization. Such activities can be assessed by one of skill in the art using any appropriate in vitro or in vivo assay.

Pharmaceutical Compositions

A PLVAP antagonist of the invention can be administered to a mammalian subject as part of a pharmaceutical or physiological composition, for example, as part of a pharmaceutical composition comprising a PLVAP antagonist and a pharmaceutically acceptable carrier. Formulations or compositions comprising a PLVAP antagonist (e.g., an antibody that specifically binds PLVAP) or compositions comprising a PLVAP antagonist and one or more other therapeutic agents (e.g., a chemotherapeutic agent, for example, doxorubicin, 5-fluorouracil, tamoxifen, octreotide) will vary according to the route of administration selected (e.g., solution, emulsion or capsule). Suitable pharmaceutical carriers can contain inert ingredients which do not interact with the PLVAP antagonist. Standard pharmaceutical formulation techniques can be employed, such as those described in Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, Pa. Suitable pharmaceutical carriers for parenteral administration include, for example, sterile water, physiological saline, bacteriostatic saline (saline containing about 0.9% mg/ml benzyl alcohol), phosphate-buffered saline, Hank's solution, Ringer's lactate and the like. Formulations can also include small amounts of substances that enhance the effectiveness of the active ingredient (e.g., emulsifying, solubilizing, pH buffering, wetting agents). Methods of encapsulation compositions (such as in a coating of hard gelatin or cyclodextran) are known in the art. For inhalation, the agent can be solubilized and loaded into a suitable dispenser for administration (e.g., an atomizer or nebulizer or pressurized aerosol dispenser).

Diagnostic Kits

The invention also provides diagnostic kits for detecting the presence of a hepatocellular carcinoma in a subject. Such kits comprise at least one agent (e.g., a nucleic acid probe, an antibody) for detecting PLVAP gene expression in a sample (e.g., a biological sample from a mammalian subject). PLVAP gene expression can be detected, for example, by detecting a PLVAP gene product, such as a PLVAP mRNA or a PLVAP protein, in the sample.

Accordingly, in one embodiment, the kit comprises at least one nucleic acid probe (e.g., an oligonucleotide probe) that specifically hybridizes to a PLVAP RNA (e.g., mRNA, hnRNA) transcript. Such probes are capable of hybridizing to PLVAP RNA under conditions of high stringency.

In another embodiment, the kit includes a pair of oligonucleotide primers that are capable of specifically hybridizing to a PLVAP gene product (e.g., mRNA, cDNA) in a sample. Such primers can be used in any standard nucleic acid amplification procedure (e.g., polymerase chain reaction (PCR), for example, RT-PCR, quantitative real time PCR) to determine the level of the PLVAP gene product in the sample.

In another embodiment, the kits of the invention include an antibody that specifically binds a PLVAP protein (e.g., a human PLVAP protein). Such antibodies include any of the PLVAP antibodies of the invention described herein. In one embodiment, the antibody comprises a V_(H) domain having the amino acid sequence of SEQ ID NO:4 and a V_(L) domain having the amino acid sequence of SEQ ID NO:9. In another embodiment, the antibody comprises a V_(H) domain having the amino acid sequence of SEQ ID NO:14 and a V_(L) domain having the amino acid sequence of SEQ ID NO:19.

The diagnostic agents in the kits of the invention can include one or more labels (e.g., detectable labels). Numerous suitable labels for diagnostic agents are known in the art and include, but are not limited to, any of the labels described herein. In a particular embodiment, the diagnostic agent (e.g., antibody) includes a radioisotope, such that agent can be used for immuno-positron emission tomography (immuno-PET).

The present invention will now be illustrated by the following Examples, which are not intended to be limiting in any way.

EXEMPLIFICATION Example 1 PLVAP Expression is Elevated in HCC Liver Tissues Relative to Non-HCC Liver Tissues Materials and Methods: Tissue Samples

Tissues of HCC and adjacent non-tumorous liver were collected from fresh specimens surgically removed from human patients for therapeutic purpose. These specimens were collected under direct supervision of attending pathologists. The collected tissues were immediately stored in liquid nitrogen at the Tumor Bank of the Koo Foundation Sun Yat-Sen Cancer Center (KF-SYSCC). Paired tissue samples from eighteen HCC patients were available for the study. The study was approved by the Institutional Review Board and written informed consent was obtained from all patients. The clinical characteristics of the eighteen HCC patients from this study are summarized in Table 1.

TABLE 1 Clinical data for eighteen HCC patients from which paired HCC and adjacent non-tumorous liver tissue samples were obtained Case HCV TNM AFP Differ- No Sex Age HBsAg HBsAb IgG Stage (ng/ml) entiation 1 M 70 + − 2  2 Moderate 2 M 75 − + + 4A 5 Well 3 M 59 + − 4A 1232 Moderate 4 F 53 + + 1  261 Moderate 5 M 45 + − 2  103 Moderate 6 M 57 + + − 2  5 Moderate 7 M 53 + + − 3A 19647 Moderate 8 M 54 − − + 3A 7 Moderate 9 M 44 + − 4A 306 Moderate 10 M 76 − − + 3A 371 Moderate 11 F 62 + − − 3A 302 Moderate 12 F 73 − − + 2  42 Moderate 13 M 46 + − 4A 563 Moderate 14 M 45 − − 3A 64435 Moderate 15 M 41 + − 2  33.9 Well 16 M 44 + + − 2  350 Moderate 17 M 67 + − 3A 51073 Moderate 18 M 34 + − 4A 2331 Moderate mRNA Transcript Profiling

Total RNA was isolated from tissues frozen in liquid nitrogen using Trizol reagents (Invitrogen, Carlsbad, Calif.). The isolated RNA was further purified using RNAEasy Mini kit (Qiagen, Valencia, Calif.), and its quality assessed using the RNA 6000 Nano assay in an Agilent 2100 Bioanalyzer (Agilent Technologies, Waldbronn, Germany). All RNA samples used for the study had an RNA Integrity Number (RIN) greater than 5.7 (8.2±1.0, mean±SD). Hybridization targets were prepared from 8 μg total RNA according to Affymetrix protocols and hybridized to an Affymetrix U133A GeneChip, which contains 22,238 probe-sets for approximately 13,000 human genes. Immediately following hybridization, the hybridized array underwent automated washing and staining using an Affymetrix GeneChip fluidics station 400 and the EukGE WS2v4 protocol. Thereafter, U133A GeneChips were scanned in an Affymetrix GeneArray scanner 2500.

Determination of Present and Absent Call of Microarray Data

Affymetrix Microarray Analysis Suite (MAS) 5.0 software was used to generate present calls for the microarray data for all 18 pairs of HCC and adjacent non-tumor liver tissues. All parameters for present call determination were default values. Each probe-set was determined as “present”, “absent” or “marginal” by MAS 5.0. Similarly, the same microarray data were processed using dChip version-2004 software to determine “present”, “absent” or “marginal” status for each probe-set on the microarrays.

Identification of Probe-Sets with Extreme Differential Expression

For identification of genes with extreme differential expression between HCC and adjacent non-tumor liver tissue, software written using Practical Extraction and Report Language (PERL) was used according to the following rules: “Tumor-specific genes” were defined as probe-sets that were called “present” in HCC and “absent” or “marginal” in the adjacent non-tumor liver tissue by both MAS 5.0 and dChip. “Non-tumor liver tissue-specific genes” were defined as probe-sets called ‘absent’ or ‘marginal’ in HCC and ‘present’ in the paired adjacent non-tumor liver tissue by both MAS 5.0 and dChip. A flowchart diagram depicting the identification algorithm is shown in FIG. 1.

Real-Time Quantitative Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR)

TaqMan™ real-time quantitative reverse transcriptase-PCR (qRT-PCR) was used to quantify mRNA. cDNA was synthesized from 8 μg of total RNA for each sample using 1500 ng oligo(dT) primer and 600 units SuperScript™ II Reverse Transcriptase from Invitrogen (Carlsbad, Calif.) in a final volume of 60 μl according to the manufacturer's instructions. For each RT-PCR reaction, 0.5 μl cDNA was used as template in a final volume of 25 μl following the manufacturers' instructions (ABI and Roche). The PCR reactions were carried out using an Applied Biosystems 7900HT Real-Time PCR system. Probes and reagents required for the experiments were obtained from Applied Biosystems (ABI) (Foster City, Calif.). The sequences of primers and the probes used for real-time quantitative RT-PCR of PLVAP are 5′-CCTGCAGGCATCCCTGTA-3′ (forward primer) (SEQ ID NO:25); 5′-CGGGCCATCCCTTGGT-3′ (reverse primer) (SEQ ID NO:26); and 5′-CCCCATCCAGTGGCTG-3′ (probe) (SEQ ID NO:27). Hypoxanthine-guanine phosphoribosyltransferase (HPRT) housekeeping gene was used as an endogenous reference for normalization. All samples were run in duplicate on the same PCR plate for the same target mRNA and the endogenous reference HPRT mRNA. The relative quantities of target mRNAs were calculated by comparative Ct method according to manufacturer's instructions (User Bulletin #2, ABI Prism 7700 Sequence Detection System). A non-tumorous liver sample was chosen as the relative calibrator for calculation.

Results:

The PLVAP gene expression intensities in 18 pairs of HCC and adjacent non-tumorous liver tissues are shown in FIG. 2. The average gene expression intensities were 759.8±436.5 and 170.6±53.4 (mean±SD) for paired HCC and adjacent non-tumorous liver tissue, respectively. The p value of paired t-test between the two groups was 2.8×10⁻⁵. These results indicate that PLVAP is expressed in HCC and not in non-tumorous liver tissue. This elevated expression of PLVAP in HCC was further confirmed when 82 unpaired HCC samples showed an average expression intensity of 810.4±482.0 (mean±SD), which is essentially the same as the finding from the 18 paired HCC samples (p=0.62 by t-test) (FIG. 2).

In order to confirm that PLVAP is significantly expressed in HCC liver tissue and not in non-tumorous liver tissue, real-time quantitative RT-PCR was performed on RNA samples from 18 pairs of HCC and adjacent non-tumorous liver tissue. Quantities of PLVAP mRNA were significantly higher in HCC relative to non-tumorous liver tissues (see FIG. 3A and Table 2). Although the results showed some overlap between two groups, PLVAP transcripts were higher in HCC than in adjacent non-tumorous liver tissue within the same individual for all individuals tested except one (FIG. 3B). This exception was likely associated with uneven degrees of RNA degradation during storage process of tissues.

TABLE 2 PLVAP gene expression intensities for 18 pairs of HCC and adjacent non-tumorous liver tissue. Expression Intensity* Sample Adjacent non-tumorous Number HCC liver tissue 1 1757 195 2 1329 210 3 1148 168 4 1130 211 5 1096 213 6 1068 181 7 932 101 8 804 60 9 630 155 10 612 175 11 607 125 12 519 146 13 478 300 14 422 180 15 275 105 16 251 204 17 251 155 18 186 184

Example 2 PLVAP is Specifically Expressed by HCC Vascular Endothelial Cells Materials and Methods: Laser Capture Microdissection (LCM) of Formalin-Fixed Paraffin Embedded Tissues

LCM of formalin fixed tissue from paraffin blocks was carried out using Arcturus PixCell® IIe system, CapSure™ HS LCM caps, and Paradise™ reagent system from Arcturus Bioscience, Inc. (Mountain View, Calif.). Seven micrometer thick tissue sections were cut, deparaffinized, rehydrated, stained and dehydrated for LCM according to manufacturer's instructions. Target cells were captured onto CapSure™ HS LCM caps using 7.5 μm laser spot size at 50 mW power and 1.3 ms duration. Approximately, 5000 to 6000 cells were captured on each cap. However, only 1000 to 2000 hepatocellular carcinoma vascular endothelial cells were captured onto each cap due to paucity of cells.

RNA Extraction from LCM Tissue Sections for Quantitative RT-PCR

Cells captured onto the CapSure™ HS LCM caps as described above were processed for RNA extraction, cDNA synthesis, in vitro transcription and antisense RNA amplification using the Paradise™ reagent system according to manufacturer's instructions. The synthesized anti-sense RNA was then used as a template for two-step TaqMan real time quantitative RT-PCR for quantitation of PLVAP and beta-actin mRNA in the cells captured by LCM. The first step (i.e., reverse transcription) was carried out using 4.5 μl anti-sense RNA and TaqMan Reverse Transcription Reagents (ABI) in a final volume of 10 μl following the manufacturer's protocol. The second step (i.e., real-time PCR) was performed using 2.4 μl of cDNA template, the primers/probe mix and the TaqMan universal PCR Master Mix from Applied Biosystems in a final volume of 25 Real-time PCR was carried out in a Smart Cycler II (Cephid, Inc., Sunnyvale, Calif.). The reactions were initially incubated at 50° C. for 2 minutes and then at 95° C. for 10 minutes. Thereafter, 45 cycles of denaturation at 95° C. for 15 seconds and annealing/extension at 60° C. for 40 seconds were performed. The sequences of the primers and the probes are listed in Table 3.

TABLE 3 Primer and probe sequences for real-time quantitative RT-PCR for PLVAP and beta-actin levels in samples prepared by laser-captured microdissection. PLVAP gene beta-Actin gene forward 5′-CCTTGAGCGTGAGTGTTTCCA-3′ 5′- primer (SEQ ID NO: 28) GTCCCCCAACTTGAGATGTATGAA G-3′ (SEQ ID NO: 29) reverse 5′-GGCAGGGCTGGGAGTTG-3′ 5′- primer (SEQ ID NO: 30) GTCTCAAGTCAGTGTACAGGTAAG C-3′ (SEQ ID NO: 31) Taqman 5′-CTCCCAGGGAGACCAA-3′ 5′-AAGGAGTGGCTCCCCTCC-3′ probe (SEQ ID NO: 32) (SEQ ID NO: 33)

Preparation of Expression Vector for Recombinant Fusion PLVAP₅₁₋₄₂₂ Protein

Plasmid pGEM®-T Easy-PLVAP₅₁₋₄₄₂ was generated by inserting a PCR fragment encoding amino acid residues 51 to 442 of PLVAP into the pGEM®-T Easy Vector (Promega, Inc., Madison, Wis.). The PCR fragment was amplified from a cDNA clone of PLVAP from OriGene (Rockville, Md.) by using the primer set of

For construction of plasmid pET-15b-PLVAP₅₁₋₄₄₂, a cDNA fragment encoding amino acid residues 51 to 442 of PLVAP with NdeI and BamHI recognition sequences at each respective end was excised from pGEM®-T Easy-PLVAP₅₁₋₄₄₂ and inserted into pET-15b (Novagen, Inc., San Diego, Calif.). The expression construct described above was verified by DNA sequencing.

Expression and Purification of Recombinant Fusion PLVAP₅₁₋₄₄₂ Protein

For production of recombinant His-tagged PLVAP₅₁₋₄₄₂ protein (SEQ ID NO:2) (FIG. 4), Escherichia coli (Rosetta-gami2(DE3)pLysS) (Novagen) was transformed by incubating competent cells with pET-15b-PLVAP₅₁₋₄₄₂ plasmid DNA on ice for 5 min, followed by incubation in a 42° C. water bath for 30s and then again on ice for 2 min. Prior to plating on selective medium, the transformants were incubated at 37° C. while shaking at 250 rpm with SOC medium (0.5% Yeast Extract; 2% Tryptone; 10 mM NaCl; 2.5 mM KCl; 10 mM MgCl₂; 10 mM MgSO₄; 20 mM Glucose) for 60 min. Expression of His-tagged fusion protein in Rosetta-gami2(DE3pLysS Escherichia coli was induced with 1 mM isopropyl-β-D-thiogalactopyranoside for 16 hours at 30° C. Following the induction, the bacterial cells were subjected to lysis by sonication in equilibration buffer (50 mM sodium phosphate, 300 mM NaCl, pH 7) supplemented with 8 M urea and separated into soluble and insoluble fractions by centrifugation at 5,600×g for 30 minutes. For further purification of the His-PLVAP₅₁₋₄₄₂ protein, soluble fraction was loaded on a TALON® Metal Affinity Resin (Clontech, Inc., Palo Alto, Calif.), washed with equilibration buffer and eluted with elution buffer (50 mM sodium phosphate, 300 mM NaCl, pH 7, 250 mM imidazole). The His-tag of the purified fusion protein was removed by thrombin cleavage (Novagen) according to manufacturer's instructions (see FIG. 5). The resulting PLVAP₅₁₋₄₄₂ protein was recovered by extensive dialysis against PBS. To verify the identity of the recombinant PLVAP protein, a small quantity of mouse antiserum against GST-PLVAP₃₃₁₋₄₃₀ fusion protein was purchased from the Biodesign Insitute (Tempe, Ariz.). The recombinant PLVAP₅₁₋₄₄₂ protein without the His-tag was detected by Western blot analysis using this antibody, but did not react with antibodies to the His-tag. These results confirm the identity of the recombinant PLVAP protein.

Generation of Mouse Anti-Human PLVAP Serum

Purified PLVAP₅₁₋₄₄₂ recombinant protein in PBS was used to immunize 6 weeks old Balb/cByj mice. Each mouse was initially immunized with subcutaneous injection at multiple sites with a total of 14 μg PLVAP₅₁₋₄₄₂ protein in complete Freund's adjuvant (Sigma, Inc., St Louis, Mo.). Thereafter, immunization was boosted with 7 μg PLVAP₅₁₋₄₄₂ recombinant protein in incomplete Freund's adjuvant once every two weeks for three times. A week after the last boosting immunization, mice were bled for preparation of antiserum.

Enzyme-Linked Immunosorbent Assay (ELISA) Reagents and Solutions:

-   -   1. Recombinant PLVAP protein     -   2. Anti-mouse IgG-alkaline phosphatase conjugate (Cat. #:         AP124A, CHEMICON)     -   3. Coating buffer (0.137 M Sodium Chloride, 0.01 M Sodium         Phosphate Dibasic Heptahydrate, 2 mM Potassium Phosphate         Monobasic, 0.002% (0.3 mM) Sodium azide, pH 7.2-7.4)     -   4. Washing buffer (0.137 M Sodium Chloride, 0.01 M Sodium         Phosphate Dibasic Heptahydrate, 2 mM Potassium Phosphate         Monobasic, 0.2% Tween20 (Cat. P1379, SIGMA, pH 7.2-7.4)     -   5. Blocking buffer (0.137 M Sodium Chloride, 0.01 M Sodium         Phosphate Dibasic Heptahydrate, 2 mM Potassium Phosphate         Monobasic, 2% Bovine Serum Albumin (Cat. 82-045, PENTEX), 0.05%         Tween20 (Cat. P1379, SIGMA), pH 7.2-7.4)     -   6. Carbonate buffer (0.016 M Sodium Bicarbonate, 0.014 M Sodium         Carbonate 2 mM Magnesium Chloride, 0.002% (0.3 mM) Sodium Azide,         pH 9.6)     -   7. Akaline Phosphatase substrate: One 40 mg phosphatase         substrate tablet (Cat. P5994, SIGMA) dissolved in 40 ml         carbonate buffer

Procedure:

The titers of antibodies in the anti-PLVAP sera were determined using ELISA. First, the 96 well ELISA plate was coated with 50 μl of PLVAP protein dissolved in Phosphate buffered saline (PBS) containing 0.002% sodium azide (i.e., coating buffer) at a concentration in the range of 2.5 μg/ml overnight at 4° C. After three washes with 200 μl of washing buffer (PBS containing 0.05% Tween-20), each well of the coated plate was blocked with 150 μl blocking buffer (i.e., washing buffer containing 2% bovine serum albumin) at room temperature for 30 minutes. After three further washes, each well was incubated with 50 μl of diluted antiserum (serial two fold dilution from 1,000× to 128,000×) prepared in the dilution buffer for 45 minutes at room temperature. Thereafter, each well was incubated with anti-mouse IgG alkaline phosphatase conjugate at 5,000× dilution (Chemico, Inc., Temecula, Calif.) for 30 minutes at room temperature. After three washes, the bound antibodies were quantified with 100 μl alkaline phosphatase substrate (Sigma, Inc., St Louis, Mo.) and measurement of absorbance was performed at 405 nm after an incubation period of 25 to 40 min. using an ELISA plate reader.

Immunohistochemical (IHC) Detection of PLVAP in Formalin-Fixed Tissues

Six micrometer sections were cut from paraffin blocks of formalin-fixed tissues. The sections were mounted on SuperFrost plus adhesion glass slides (Menzel Glaser GmbH, Braunschweig, Germany). The sections then were processed for immunostaining of PLVAP in a Benchmark XT automated staining instrument (Ventana Medical Systems, Inc., Tucson, Ariz.) using XT-iView-DAB-V.1 protocol with mild CCI conditioning for 30 minutes and sections were incubated with 400× diluted anti-human PLVAP serum at 37° C. for 36 minutes. The second antibody and the reagents used to detect binding of mouse anti-human PLVAP antibodies were from the iView™DAB Detection Kit from Ventana Medical Systems, Inc. (Tucson, Ariz.). All reagents and buffers were purchased from Ventana Medical Systems.

Results:

To determine the cellular source of PLVAP in HCC samples, HCC vascular endothelial cells, tumor cells of hepatocellular carcinoma and non-tumorous hepatocytes, including lining sinusoidal endothelial cells, were dissected out of the samples using laser capture microdissection (LCM). Due to close apposition between hepatoma cells and capillary-lining endothelial cells, effort was made to avoid inclusion of capillary-lining endothelial cells during dissection. The RNAs extracted from the dissected cells were used for two-step real time quantitative RT-PCR to determine the relative quantities of PLVAP mRNA. Specimens from two different patients were studied. The results shown in Table 4 and FIGS. 6A-C indicate that PLVAP is expressed by HCC vascular endothelial cells (FIG. 6A), while no detectable PLVAP transcript was detected in adjacent non-tumorous liver tissues (FIG. 6B).

TABLE 4 Determination of PLVAP mRNA relative quantities in two HCC samples by Taqman real time quantitative RT-PCR in cells dissected by laser-capturing microdissection Relative Quantity of PLVAP mRNA HCC Endothelial Adjacent Non-tumorous HCC Tumor HCC Sample Cells Liver Tissue Cells A 1 0 0.002 B 1 0.001 0.057

In order to further investigate the tissue and disease specificity of PLVAP expression, polyclonal antibodies for use in immunohistochemistry (IHC) studies were generated against the extracellular domain of human PLVAP (amino acids 51 to 442). As shown in FIG. 7, antiserum obtained from Balb/c mice that were immunized with recombinant PLVAP₅₁₋₄₄₂ protein contained a high titer of anti-PLVAP antibodies.

The anti-PLVAP antiserum was then used to determine the localization of PLVAP expression in tissue sections from patients with hepatocellular carcinoma (n=7) (FIGS. 8A-F and 9A-F), focal nodular hyperplasia (n=4) (FIGS. 10A-F), hepatic hemangioma (n=2) (FIGS. 11A and B), chronic active hepatitis B (n=2) (FIGS. 12A and B) or C (n=4) (FIGS. 13A-D), and metastatic cancer (n=4) (i.e., intrahepatic cholangiocarcinoma, metastatic colorectal adenocarcinoma, or metastatic ovarian carcinoma) (FIGS. 14A-D). The results showed that only capillary endothelial cells of hepatocellular carcinomas expressed PLVAP protein (FIGS. 8A,C,E and 9A,C,E,F). PLVAP protein was not expressed by endothelial cells lining the vascular sinusoids/capillary of non-tumorous liver tissues including cirrhotic liver, liver of focal nodular hyperplasia (FIGS. 10A-F), and chronic hepatitis (FIGS. 12A and B; FIGS. 13A-D). Endothelial lining cells of hepatic hemagioma did not show significant expression of PLVAP, either (FIGS. 11A and B). These results demonstrate that PLVAP is a vascular endothelial biomarker that is specific for hepatocellular carcinoma, but not for other diseases of liver. Therefore, PLVAP can be used as a diagnostic marker and therapeutic target for HCC.

Example 3 Production and Characterization of Mouse Monoclonal Antibodies that Specifically Bind PLVAP Materials and Methods Immunization Procedures

Five six-week-old female Balb/cByJ mice were immunized initially with 20 μg of purified recombinant PLVAP protein dissolved in 0.125 mL phosphate buffered saline (PBS) and emulsified in an equal volume of complete Freund's adjuvant. The PLVAP-adjuvant mixture was injected in 0.05 mL volumes into each of four separate subcutaneous sites on the ventral side of the mice near the axillary and inguinal lymphatics, as well as a fifth subcutaneous site, which was located between the scapulae. All mice received a booster immunization of 20 μg of recombinant PLVAP protein injected intraperitoneally three times every two weeks. One week after the last booster immunization, test bleedings were taken to measure whether mice were producing sufficiently high titers of anti-PLVAP antibodies (>10,000×). A solid-phase enzyme-linked immunosorbent assay (ELISA) was used for this purpose. The mouse that produced the highest titer of PLVAP antibody was selected for the production of hybridomas.

Development of Murine Monoclonal Anti-PLVAP Antibodies

Three days before the scheduled fusion experiment to produce hybridomas, the mouse that produced the highest titer of PLVAP antibody was injected intravenously with 20 μg of recombinant PLVAP. Hybridomas producing monoclonal antibodies (MAbs) against PLVAP were produced according to a previously described protocol (see Unit 2.5 Production of Monoclonal Antibodies, in Current Protocols in Immunology, editors: Coligan J E, Kruisbeek A M, Margulies D H, Shevach E M, and Strober W. Published by John Wiley & Sons, Inc., New York, 2001) with minor modification. Specifically, spleen cells harvested from the immunized mouse were fused with SP2/0 myeloma cells at a ratio of 7.5:1 (spleen cell: myeloma cells) using 50% polyethylene glycol 1540. The fusion products were seeded into 96-well flat-bottom tissue culture plates, and hypoxanthine-aminopterin-thymidine (HAT) selective medium was added the next day. Seven to ten days later, the supernatants of growth-positive wells were screened for production of anti-PLVAP antibodies by ELISA. Hybridomas initially producing anti-PLVAP MAbs were expanded and re-screened. Hybridomas that showed continued production of antibodies were cloned by the limiting dilution method. MAb isotypes were determined using an ELISA. Monoclonal antibodies were purified from ascites or culture media by Protein G affinity column chromatography (Unit 2.7 Purification and Fragmentation of Antibodies, in Current Protocols in Immunology, editors: Coligan J E, Kruisbeek A M, Margulies D H, Shevach E M, and Strober W. Published by John Wiley & Sons, Inc., New York, 2001).

ELISA Assay

Elisa assays were performed as described herein (see Example 2).

Determination of Binding Affinities

Binding affinities of KFCC-GY4 and KFCC-GY5 anti-PLVAP monoclonal antibodies were measured at the ANT Technology Co., Ltd. (Taipei, Taiwan) using ANTQ300 quartz crystal microbalance technology (Lin S., et al. J Immunol Methods 239:121-124 (2000)).

Isolation and Culture of Human Umbilical Vascular Endothelial Cells (HUVEC)

Isolation and culture of HUVEC were carried out according to the established protocol described in Baudin B, Brunee A, Bosselut N and Vaubourdolle M. Nature Protocols 2:481-485 (2007). During the maintenance of endothelial cell culture, 1% gelatin (DIFCO, Corp.) dissolved in phosphate buffered saline was used to replace collagen solution for coating culture plates or coverslips.

Extraction of Hydrophobic Membrane Proteins of HUVEC by Triton X-114 (TX-114) Containing Buffer

Five hundred thousand HUVEC were seeded in a 10 cm culture dish for 24 hours. The cells were then stimulated with human VEGF at 40 ng/ml for an additional 72 hours. The cultured cells were washed with 5 ml phosphate buffered saline (PBS) twice. The cells then were detached and lifted from the dish by incubation with 1 ml PBS containing 2 mM EDTA, were placed into a centrifuge tube, and were collected by centrifugation at 300×g for 5 minutes. There were approximately 2 million cells in the pellet produced by centrifugation. The cell pellets were re-suspended in 200 μl ice cold 0.05 M Tris buffer, containing 5 mM EDTA and 0.5% (v/v) Triton X-114 (TX-114), pH 7.4. The solubilized cell suspension was incubated on ice with occasional gentle vortexing. Thereafter, the cells suspension was centrifuged at 10,000×g for 10 minutes at 4° C. to remove insoluble cellular debris. The supernatant was transferred to a clean microfuge tube and incubated at 37° C. for 5 minutes. During the incubation TX-114 became separated from the aqueous phase. The microfuge tube was then centrifuged at 1000×g for 10 minutes at room temperature, such that the TX-114 was centrifuged to the bottom of the tube. The aqueous phase at the top of the tube was removed and the TX-114 pellet containing hydrophobic cellular proteins was dissolved in 2×SDS acrylamide gel sample buffer in a final volume of 50 μl. Fifteen μl of sample was used for SDS acrylamide gel electrophoresis.

SDS Acrylamide Gel Electrophoresis, Preparation of Western Blot and Immunoblotting

The procedures are the same as previously described by Kao K J, Scornik J C and McQueen C F. Human Immunol 27:285-297 (1990), with slight modification.

Detection of antibody binding on Western blots was carried out using alkaline phosphatase chemiluminescent substrate and an LAS-4000 Luminescent Image Analyzer (Fujifilm Corp.)

Immunofluorescent Microscopy Materials:

-   1). Primary antibodies:     -   a). Normal mouse IgG (Sigma Corp., catalog #:I-5381) dissolved         in phosphate buffered saline (PBS) to 1 mg/mL as a stock         solution, diluted with PBS-0.5% BSA to a concentration of 5         μg/mL before use;     -   b.) Monoclonal mouse anti-human von Willebrand factor (vWF)         (DakoCytomation Corp., catalog #:M0616) diluted 50× with PBS         containing 0.5% BSA before use;     -   c.) Purified KFCC-GY4 and KFCC-GY5 anti-PLVAP monoclonal         antibodies were diluted to 5 μg/ml with PBS containing 0.5% BSA         before use; -   2). Secondary antibody: FITC-conjugated Goat F(ab′)₂ anti-mouse IgG     (H&L) (Serotec, Corp., catalog #: Star105F); -   3). VectaShield Mounting Medium with DAPI (Vector Labs, Corp.,     catalog #: H-1200); -   4). 100% Methanol (Merck corp. catalog #:1.06009); and -   5). Hank's Balanced Salt Solution (HBSS) (Gibco, Corp., catalog     #:12065-056) diluted to 1× before use.

Procedure:

To prepare human umbilical cord vascular endothelial cells for immunofluorescent study, fifty thousand cells were placed in each well of a 24-well culture plate with a 1.5 cm sterile round coverslip placed at the bottom of each well. Each well contained 0.5 ml M199 culture media that was supplemented with 20% fetal calf serum, 1% L-glutamine, 1% antibiotic/antimycotic solution, 50 μg/ml heparin and 75 μg/ml endothelial cell growth supplement (Sigma, Corp. E0760). Each coverslip was pre-coated with 200 μl of 0.4 mg/ml calf skin collagen (Sigma Corp. C9791) in 0.04% acetic acid (v/v) overnight. The coverslips were then washed with sterile 1× phosphate buffered saline (PBS), and subsequently air-dried for use. Cells were cultured overnight and then stimulated with 40 ng/ml vascular endothelial growth factor (VEGF) for an additional 72 hours. The cells on the coverslips were used for the immunofluorescent procedure.

To stain the cells for immunofluorescent microscopy, the cells grown on the coverslip in each well were washed with 0.5 ml 1×HBSS. The cells were then fixed and permeabilized in 0.5 ml ice cold methanol for 5 minutes. The fixed cells were washed 3 times with 0.5 ml 1×PBS for 5 minutes per wash. The fixed cells were then blocked with 0.5 ml 1×PBS containing 0.5% BSA for 1 hour at room temperature. The coverslip containing the fixed cells was removed and placed on top of 0.2 ml diluted primary antibody solution, which contained 5 μg/ml normal IgG, KFCC-GY4 or KFCC-GY5 anti-PLVAP monoclonal antibody, or a 50× dilution of anti-human vWF monoclonal antibody, with the fixed cells facing down and in contact with antibody solution. The antibody solution was placed on a piece of parafilm in a small covered plastic container. The humidity inside was maintained by placing a small piece of filter paper wetted with water.

After incubation at 37° C. for one hour in a humidified container, the coverslip was removed and the cells on the coverslip were washed 3 times with 0.5 ml PBS for 5 minutes each time. The fixed cells were then incubated with 0.2 ml 200×-diluted FITC-conjugated Goat F(ab′)₂ anti-mouse IgG secondary antibody for 50 minutes at 37° C. as described for incubation with primary antibody solution. Thereafter, the cells were washed 3 times with PBS as described above. The stained cells were mounted on a glass slide using VectaShield anti-fade solution. Excess mounting media was removed from the edge of the coverslip and the edge was sealed with nail polish. The stained cells were examined using a fluorescent microscope.

Results

Immunization of Balb/cByJ mice with recombinant human PLVAP protein led to the development of hybridomas producing monoclonal antibodies (mAbs) that recognized human PLVAP protein. Two hybridomas were selected for further study. The antibodies produced by these hybridomas were named KFCC-GY4 and KFCC-GY5. The sequences of the V_(H) and V_(L) domains of monoclonal antibodies KFCC-GY4 and KFCC-GY5, and the CDRs of these domains, are shown in FIGS. 15A and B, and 16A and B, respectively.

The hybridoma cell line referred to as KFCC-GY4 has the A.T.C.C. Patent Deposit Designation PTA-9963, having been deposited on Apr. 8, 2009. The hybridoma cell line referred to as KFCC-GY5 has the A.T.C.C. Patent Deposit Designation PTA-9964, having been deposited on Apr. 8, 2009.

Both KFCC-GY4 and KFCC-GY5 monoclonal antibodies bound recombinant PLVAP protein in ELISA (FIG. 17) and immunoblot (FIGS. 18C and D) assays.

These antibodies also specifically reacted with PLVAP protein in extracts from human umbilical cord vascular endothelial cells in an immunoblot assay (FIGS. 19B and D). In addition, immunofluorescence staining experiments showed binding of KFCC-GY4 and KFCC-GY5 monoclonal antibodies to PLVAP-expressing human vascular endothelial cells (FIGS. 20C and D).

Binding affinities (K_(d)) of the monoclonal antibodies for recombinant PLVAP protein were determined to be 0.41×10⁻⁷ M for KFCC-GY5 mAb and 0.6×10⁻⁷M for KFCC-GY4 mAb using ANTQ300 quartz crystal microbalance (Lin, et al. J. Immunol. Methods 239:121-124, 2000).

Immunohistochemistry experiments performed on hepatoma sections from the liver of two different hepatoma patients using KFCC-GY4 or KFCC-GY5 monoclonal anti-PLVAP antibodies showed that the KFCC-GY5 monoclonal antibody produced a stronger signal in vascular endothelial cells (FIGS. 21A,C) than the KFCC-GY4 monoclonal antibody (FIGS. 21B,D).

Immunohistochemistry experiments performed on adjacent hepatoma and non-tumorous liver tissue sections from the liver of the same patient were performed on samples from four different randomly selected hepatoma patients using the KFCC-GY4 monoclonal anti-PLVAP antibody. PLVAP expression was detected in vascular endothelial cells of hepatoma tissues (FIGS. 22A, C, E, and G), but not adjacent non-tumorous liver tissues (FIGS. 22B, D, F, and H).

Example 4 PLVAP Protein is Expressed on the Surfaces of Vascular Endothelial Cells Materials and Methods Immunofluorescent Microscopy Reagents:

The reagents used for the following procedure are as described in Example 3, with the following modifications:

-   -   the 1×HBSS wash buffer contained 0.1% sodium azide, which was         used to prevent endocytosis of antibodies bound to the cell         surface;     -   the KFCC-GY4 and KFCC-GY5 monoclonal anti-PLVAP antibodies were         diluted in the 1×HBSS wash buffer with 0.1% sodium azide;

Procedure:

Immunofluorescent staining of human umbilical cord vascular endothelial cells (HUVECs) was performed as described in Example 3, except that the cells were not fixed and permeabilized with methanol. Instead, after incubation with anti-PLVAP monoclonal antibodies, the cells were washed and fixed with 4% paraformaldehyde at room temperature for 10 minutes. Following this incubation, the cells were washed 3 times, then were incubated with FITC-conjugated Goat F(ab′)₂ anti-mouse IgG. After three additional washes, the cells were processed for immunofluorescent microscopy as described in Example 3.

Results

Using the approach described above, only PLVAP protein expressed on the cell surface could be detected. The results of these experiments revealed that both KFCC-GY4 and KFCC-GY5 anti-PLVAP monoclonal antibodies bound to the surface of HCC vascular endothelial cells (FIGS. 23B,C), indicating that PLVAP protein is expressed on the surfaces of these cells. These findings suggest that antibodies that specifically bind PLVAP with high affinity will be able to bind to the surface of HCC vascular endothelial cells upon injection into the blood vessels of a hepatocellular carcinoma tumor.

Example 5 Anti-Human PLVAP Monoclonal Antibodies Bind to PLVAP Proteins in Non-Human Primate Species Materials and Methods

Tissue array slides were first prepared according to manufacturer's instructions by baking slides at 60° C. for 2 hours to remove sealing paraffin. Thereafter, the slides were processed for immunohistochemical staining as described in Example 2 (IHC detection of PLVAP in formalin fixed tissues). The only modification was that the slides were incubated with 1 μg/ml KFCC-GY4 and -GY5 monoclonal antibodies for 48 minutes at 37° C.

Results

In order to determine whether non-human primates can be used to evaluate the pharmacokinetics, pharmacodynamics and toxicity of the KFCC-GY4 and KFCC-GY5 mAbs, as well as other antibodies derived from these mAbs, immunohistochemistry staining of arrays of formalin-fixed normal tissues from human, rhesus monkey and cynomolgus monkey were performed using the KFCC-GY4 and KFCC-GY5 antibodies (FIG. 26). The KFCC-GY4 and KFCC-GY5 anti-human PLVAP monoclonal antibodies bound to both human and monkey (cynomolgus and rhesus) capillary endothelial cells in different tissues with high degree of similarity (FIG. 26). Examples of KFCC-GY5 antibody binding to human and monkey normal adrenal gland, kidney, brain and liver sections are shown in FIGS. 27A-F2. Anti-human CD34 monoclonal antibody was also used as a positive control on human tissue sections to highlight blood vessels. These results indicate that rhesus and cynomolgus monkeys are suitable for use in pre-clinical trial studies of PLVAP antibodies.

Example 6 KFCC-GY4 and KFCC-GY5 Monoclonal Antibodies Bind to Antigenic Epitopes Between Amino Acids 282 and 482 in the C-Terminal Region of Human PLVAP Protein Materials and Methods Molecular Cloning

Plasmids expressing His-tagged N-terminal (amino acids 51-292) or C-terminal (amino acids 282-442) portions of the extracellular domain of human PLVAP (amino acids 51-442) were constructed as follows. pGEM®-T Easy-PLVAP₅₁₋₄₄₂ was treated with Eco RV and Stu I, self-ligated and generated the resulting plasmid pGEM®-T Easy-PLVAP₅₁₋₂₉₂. For construction of plasmid pET-15b-PLVAP₅₁₋₂₉₂, a cDNA fragment representing the amino acid residues 51 to 292 of PLVAP with NdeI/BamHI recognition sequences at the ends was excised from pGEM®-T Easy-PLVAP₅₁₋₂₉₂ and inserted into pET-15b (Novagen). To construct pET-15b-PLVAP₂₈₂₋₄₄₂, pET-15b-PLVAP₅₁₋₄₄₂ was treated with Nde I and Sac I, followed by blunt-end ligation using T4 DNA polymerase. The expression constructs described above were verified by DNA sequencing and transformed into Escherichia coli (Rosetta-gami2(DE3)pLysS).

Recombinant Protein Expression and Immunoblotting

Expression of His-tagged fusion proteins in Escherichia coli Rosetta-gami2(DE3)pLysS cells was induced with 1 mM isopropyl-β-D-thiogalactopyranoside for 16 hours at 30° C. Following the induction, the bacterial cells were subjected to lysis by Laemmli sample buffer. The resultant cell lysates were resolved by SDS-PAGE and subjected to Coomassie blue staining and immunoblotting using standard protocols and the following antibodies: primary antibodies: KFCC-GY4, KFCC-GY5, mAb 2A7-6, anti-his mAb (LTK Biotechnology, Taiwan). Immunoblots were developed by alkaline phosphatase-conjugated secondary antibodies against mouse IgG from Chemicon, Inc. using standard procedure.

PCR Amplification and Library Screening

The primers PLVAP Sac I F: 5′-CTCCAAGGTGGAGGAGCTGGC-3′ (SEQ ID NO:36), and PLVAP Stop Bam HI R:

5′-GGATCCTGAGCATATCCCTGCATCCTCC-3′ (SEQ ID NO:37) were used to amplify the sequence coding for the C-terminal portion of the PLVAP (amino acids 282-442) extracellular domain. PCR was performed using the following thermal cycle: 94° C. for 5 min, followed by 35 cycles of 94° C. for 30 s, 56° C. for 30 s and 72° C. for 60 s. DNA was purified with the Qiaquick PCR purification kit (Qiagen, Surrey, UK) and then used in the construction of a PLVAP Novatope library according to the manufacturers instructions (Novagen, Merck Biosciences Ltd., Beeston, UK). Briefly, purified PCR product was digested with DNAse I in the presence of Mn²⁺ and fragments between 50-150 base pairs (bp) were gel purified using a gel extraction kit (Qiagen). The DNA fragments were end-filled using T4 DNA polymerase and Tth polymerase to add a single dA residue to each 3′ end, and then ligated into the pScreen 1b(+)T-vector (Novagen), which is designed to express small inserts as a carboxy-terminal fusion to the T7 bacterial phage gene 10 capsid protein. The library was transformed into NovaBlue(DE3) cells and plated onto Luria-Bertani (LB) media plates containing carbenicillin (50 μg/ml) and tetracycline (12.5 μg/ml). The resulting human PLVAP cDNA library was screened (approximately 10⁴ colonies for each antibody) using the method described in the Novatope manual: Colonies expressing PLVAP fragments were transferred to nitrocellulose filters by contact with the colony for 1 min. Bacterial colonies on the filters were lysed by incubating in a sealed chloroform vapor chamber for 15 min. Proteins were denatured in colony denaturing solution (20 mM Tris pH 7.9, 6 M Urea, 0.5 M NaCl) for 15 min and the filters were blocked for 30 min in 1% (w/v) gelatin in TBS with 0.05% (v/v) Tween 20 (TBS-T). Colony debris was removed by wiping with a tissue and then the filters were probed for 1 h with monoclonal antibody KFCC-GY4 and KFCC-GY5 (1 μg/ml) in TBS-T with 0.5% (w/v) gelatin. Blots were washed for 15 min twice in TBS-T with 0.5% (w/v) gelatin and then probed with a 1/5000 dilution of goat-anti mouse immunoglobulin-alkaline phosphatase conjugate (Chemicon) in TBS-T with 0.5% (w/v) gelatin. After washing, blots were developed using bromo-4-chloro-3-indolylphosphate/nitroblue tetrazolium (BCIP; 33 μg/ml; NBT; 66 μg/ml) substrate (Sigma). Positive colonies from each screen were plated onto fresh LB amp/tet plates and then re-probed with monoclonal antibody. Confirmed positives were used in DNA minipreps and the PLVAP gene inserts were sequenced using T7 terminator primer.

ELISA for Study of Binding Interference

Each well of an ELISA plate was coated with 50 μl KFCC-GY5 anti-PLVAP monoclonal antibodies at a concentration of 5 μg/ml in PBS overnight. After blocking and washing, 50 μl of recombinant PLVAP protein (0.5 μg/ml) was added to each well. After incubation at room temperature for 60 minutes, the wells were washed and 50 μl of biotinylated KFCC-GY4 antibody at different concentrations was added to each well in duplicates and incubated for 30 minutes. After three washings, the wells were developed with 50 μl of diluted streptavidin-horseradish peroxidase conjugate and substrate. Optical density at 450 nm was measured for each well. Each value was a mean of duplicates.

ELISA for Additive Binding

Each well of an ELISA plate was coated with 50 μl of 0.25 μg/ml recombinant PLVAP protein. The wells were blocked and incubated with 50 μl of each humanized antibody derived from KFCC-GY4 or KFCC-GY5, either separately or together. The final concentration of each antibody was 0.01 μg/ml. The values were an average of duplicates.

Results

To characterize the KFCC-GY4 and KFCC-GY5 mAbs further, epitope mapping was conducted to determine the antigenic sites in PLVAP that are bound by each of these antibodies. Initial results demonstrated that the antigenic epitopes for both antibodies reside in the C-terminal region of PLVAP protein between amino acids 282 and 482 (FIGS. 28A, 28B and 28C). Both KFCC-GY4 and KFCC-GY5 mAbs reacted positively with PLVAP₅₁₋₄₄₂ (lane 1) and PLVAP₂₈₂₋₄₄₂ (lane 2), but did not react with PLVAP51-292 (lane 3) or human CEACAM6 protein unrelated to PLVAP (lane 4). The results indicate that the epitopes for both antibodies reside in the C-terminal end of PLVAP between amino acid residues 292 to 442.

A finer mapping study revealed that the KFCC-GY4 mAb reacted with an E. coli clone expressing a peptide encompassing amino acids 431 to 442 of human PLVAP and the KFCC-GY5 mAb reacted with an E. coli clone expressing a peptide encompassing amino acids 378 to 404 of human PLVAP. As depicted in Table 5, the epitopes for these two mAbs do not overlap.

TABLE 5 Antigenic epitopes for KFCC-GY4 and KFCC-GY5 monoclonal antibodies Amino acid sequence responsible for antigenic epitope for KFCC-GY4 mAb: Human 431 SQRPPAGIPVAPSSG 442 (SEQ ID NO: 38) Mouse 426 SQRLPVVNPAAQPSG 437 (SEQ ID NO: 39) Amino acid sequence responsible for antigenic epitope for KFCC-GY5 mAb: Human 378 ELAIRNSALDTCIKTKSQPMMPVSRPM 404 (SEQ ID NO: 40) Mouse 375 EVDVRISALDTCVKAKSLPAVP-PRVS 400 (SEQ ID NO: 41)

The KFCC-GY4 and KFCC-GY5 mAbs could each bind to human PLVAP in an enzyme-linked immunoassay (ELISA) without interfering with the binding of the other antibody (FIG. 29). This lack of interference was also observed using fully humanized composite KFCC-GY4 and KFCC-GY5 monoclonal antibodies (FIG. 30), which are described in more detail below.

Example 7 Production and Characterization of Chimeric Antibodies that Specifically Bind PLVAP Materials and Methods Abbreviations

Abbreviation Description CDR Complementarity Determining region of an antibody variable region (numbered CDR1-3 for each of the heavy and light chains, as defined by Kabat). Ec(0.1%) The Absorbance of a 1 mg/ml solution of protein ELISA Enzyme linked immunosorbent assay FW Framework region - scaffold region of a variable domain supporting the CDRs HRP Horse-radish peroxidase IgG Immunoglobulin G mAb Monoclonal antibody OD280nm Optical density measured at 280 nm P protein PLVAP protein PBS Phosphate-buffered saline TMB 3,3′,5,5′-tetramethylbenzidine V-region Variable region of an antibody chain

Initial Determination of Variable Region Sequences

Total RNA was extracted using Trizol reagent (Invitrogen, Carlsbad, Calif.) from 2×10⁷ cultured hybridoma cells from the cell lines KFCC-GY4 and KFCC-GY5. 5′ RACE was carried out using the FirstChoice RLM-RACE kit (Ambion, Inc., Austin, Tex.) following the manufacture's instructions to determine the coding sequence of VH and VL domains from KFCC-GY4 and KFCC-GY5. Briefly, 10 μg of extracted RNA was treated with calf intestinal phosphatase (CIP) in a 20 μl total volume reaction mixture containing 2 μl of 10×CIP buffer and 2 μl of CIP for 1 h at 37° C. After extracted with phenol/chloroform, RNA was precipitated with ethanol and resuspended in 11 μl of nuclease-free water. 5 μl of CIP-treated RNA was treated with tobacco acid pyrophosphatase (TAP) in a 10 μl reaction mixture containing 1 μl of 10×TAP buffer and 2 μl of TAP for 1 h at 37° C. 2 μl of the CIP/TAP-treated RNA was then ligated to 300 ng of RNA adaptor by T4 RNA ligase in a 10 pt reaction mixture for 1 h at 37° C. 2 μl of the ligated RNA or control RNA was used as a template to synthesize cDNA with M-MLV reverse transcriptase for 1 h at 42° C. using random decamers. The cDNAs corresponding to variable heavy (VH) and light (VL) chains were then amplified by PCR separately with Takara Ex Taq DNA polymerase (Takara Bio Inc., Osaka, Japan) using forward 5′ RACE outer primer 5′-GCTGATGGCGATGAATGAACACTG-3′ (SEQ ID NO:42) and reverse primers complementary to the nucleotide sequences encoding the kappa chain constant region (5′-TCAACGTGAGGGTGCTGCTCATGC-3′) (SEQ ID NO:43) or the heavy chain CH1 region (5′-TTTCTTGTCCACCTTGGTGCTGCTGG-3′) (SEQ ID NO:44), respectively. The PCR reaction mixtures were incubated for 5 min at 94° C. followed by 35 amplification cycles, comprising denaturation at 94° C. for 30 s, annealing at 57° C. for 30 s and extension at 72° C. for 1 min. The reaction was extended for another 7 min at 72° C. to insure full extension. PCR products were analyzed and purified from the 1.5 agarose gel using the Qiaquick gel extraction kit (Qiagen, Mississauga, Ontario, Canada). The purified PCR fragments were cloned into the plasmid vector, pGEM-T-easy (Promega, Madison, Wis., USA). A minimum of 5 independent clones for each chain were subjected to nucleotide sequencing analysis. The CDRs were identified according to Kabat definition (FIGS. 15A,B and 16A,B).

Independent Confirmation of Variable Region Sequences

mRNA was successfully extracted (Promega Catalogue No. Z5400) from frozen KFCC-GY4 and KFCC-GY5 cells. RT-PCR was performed using degenerate primer pools for murine signal sequences with a single constant region primer. Heavy chain variable region mRNA was amplified using a set of six degenerate primer pools (HA to HF) and light chain variable region mRNA was amplified using a set of seven degenerate primer pools (kappaA to kappaG)—monoclonal isotyping analysis of the IgGs using Roche Isostrips (Roche Catalogue No. 493027001) revealed them both to be IgG1/kappa isotypes. Amplification products were obtained with heavy chain and kappa light chain primer pools confirming the light chain is from the kappa cluster. Each product was cloned and several clones from each sequenced. For KFCC-GY4 and KFCC-GY5 antibodies, single functional heavy and light chain variable region sequences were identified for each antibody.

Expression of Chimeric Antibodies

The KFCC-GY4 and KFCC-GY5 variable regions were transferred to an expression vector system (Antitope) for IgG4 heavy chain and kappa light chain. NS0 cells were transfected via electroporation and selected using methotrexate. A number of methotrexate resistant colonies were identified and cell lines positive for IgG expression were expanded. Genomic DNA from the lead cell lines was recovered and subjected to PCR and confirmatory sequencing. IgG chimeric KFCC-GY4 and KFCC-GY5 IgG4s were purified from cell culture supernatants on a Protein A sepharose column (GE Healthcare Catalogue No. 110034-93) and quantified by OD280 nm using an extinction coefficient, Ec(0.1%), based on the predicted amino acid sequence—Ec(0.1%) values of 1.484 and 1.334 were used for chimeric KFCC-GY4 and KFCC-GY5 respectively. Greater than 2 mg of antibody was purified and analyzed by SDS-PAGE (FIG. 31). Bands corresponding to the predicted sizes of the heavy and light chains were observed with no evidence of any contamination.

Binding of Chimeric KFCC-GY4 and KFCC-GY5 Antibodies to Recombinant PLVAP

The binding of chimeric KFCC-GY4 and KFCC-GY5 antibodies to recombinant PLVAP protein was assessed in a competition ELISA. A dilution series of chimeric or control antibody from either 30 μg/ml to 0.014 μg/ml (final concentration) was premixed with a constant concentration of biotinylated murine KFCC-GY4 (0.3 μg/ml, final concentration), or 10 μg/ml to 0.004 μg/ml (final concentration) was premixed with a constant concentration of biotinylated murine KFCC-GY5 (0.1 μg/ml, final concentration), before incubating for 1 hour at room temperature on a Nunc Immuno MaxiSorp 96 well flat bottom microtitre plate (Fisher Catalogue No. DIS-971-030J) precoated with 1 μg/ml recombinant PLVAP protein diluted in PBS. The binding of the biotinylated mAb was determined by detection with streptavidin-HRP and TMB substrate.

Results

Variable regions from the KFCC-GY4 and KFCC-GY5 mouse anti-PLVAP monoclonal antibodies were successfully cloned and sequenced. Three complementarity determining regions (CDRs) were identified in each antibody according to Kabat definition. The analysis of the sequences obtained from hybridomas KFCC-GY4 and KFCC-GY5 from the confirmation studies are summarized in Tables 6 and 7. These sequences matched the sequences obtained by the initial characterization (FIGS. 15A,B and 16A,B), with the exception of a single silent mismatch in the KFCC-GY4 light chain nucleotide sequence. The aberrant transcript (GenBank accession number M35669) normally associated with the hybridoma fusion partner SP2/0 was also detected in both cell lines.

TABLE 6 Sequence analysis of KFCC-GY4 monoclonal antibody H Chain L Chain CDR 1 Length 5aa 16aa CDR 2 Length 17aa 7aa CDR 3 Length 4aa 9aa Closest Human IGHV1-f*01 (64%) IGKV2D-30*01 (82%) Germline^(b) Closest Human FW1^(b) IGHV1-46*03 (68%) IGKV2D-29*02 (87%) Closest Human FW2^(b) IGHV7-4-1*03 (71%) IGKV2D-30*01 (80%) Closest Human FW3^(b) IGHV1-f*01 (70%) IGKV2D-40*01 (94%) Closest Human J^(b) IGHJ6*01 (91%) IGKJ4 (90%) Max no. mouse FR 13 (4) 4 (1) residues^(c)

TABLE 7 Sequence analysis of KFCC-GY5 monoclonal antibody H Chain L Chain CDR 1 Length 5aa 16aa CDR 2 Length 17aa 7aa CDR 3 Length 4aa 9aa Closest Human IGHV1-46*03 (68%) IGKV2D-29*02 (80%) Germline^(b) Closest Human FW1^(b) IGHV7-4-1*02 (76%) IGKV2D-30*01 (83%) Closest Human FW2^(b) IGHV7-4-1*02 (79%) IGKV2D-40*01 (93%) Closest Human FW3^(b) IGHV1-69*10 (72%) IGKV2D-40*01 (91%) Closest Human J^(b) IGHJ6*01 (91%) IGKJ2 (90%) Max no. mouse FR 9 (3) 2 (2) residues^(c) ^(a)CDR definitions and sequence numbering according to Kabat ^(b)Germline ID(s) indicated followed by % homology ^(c)Indicates maximum number of mouse residues that need to be sourced from human sequence segments with number of those potentially critical for affinity indicated in brackets

Variable region genes were then combined with human IgG4 heavy chain and kappa light chain constant regions and expressed in NS0 cells to produce chimeric anti-PLVAP antibodies. To accomplish this, plasmid vectors carrying KFCC-GY4 chimeric heavy and light chains, and KFCC-GY5 chimeric heavy and light chains were constructed (FIGS. 32A-C, 33A,B, 34A-C and 35A,B). These plasmids were used to transfect NSO cells. Stably transfected and chimeric antibody-producing cells were cloned.

The heavy and light chain variable regions for the KFCC-GY4 antibody show good homology to their closest human germline sequences (64% and 80% respectively for KFCC-GY4) and the individual framework sequences have close homologues in the human germline database. This therefore reduces the extent of engineering that needs to be undertaken for a successful humanized antibody. The maximum number of mouse framework residues that will need to be sourced from human sequence segments for the KFCC-GY4 heavy chain is 13, with 4 constraining residues probably being crucial for maintenance of binding activity. The maximum number of mouse framework residues that will need to be sourced from human sequence segments for the KFCC-GY4 light chain is 4, with 1 constraining residue thought to be critical for activity (Table 6).

The heavy and light chain variable regions for the KFCC-GY5 antibody also showed good homology to their closest human germline sequences (68% and 80% respectively for KFCC-GY5) and the individual framework sequences have close homologues in the human germline database. This therefore reduces the extent of engineering that needs to be undertaken for a successful humanized antibody. The maximum number of mouse framework residues that will need to be sourced from human sequence segments for the heavy chain is 9, with 3 constraining residues probably being crucial for maintenance of binding activity. The maximum number of mouse framework residues that will need to be sourced from human sequence segments for the light chain is 2, with both thought to be critical for activity (Table 7). Composite Human Antibody™ analysis (Antitope; Cambridge, UK) revealed that human framework segments can be found to include all desirable mouse residues and therefore complete humanized antibodies can be built from both templates.

A competition ELISA assay was used to demonstrate that the binding efficiencies of the chimeric antibodies for PLVAP are similar to that of the respective parent murine antibodies. The chimeric IgG4-GY4 and murine KFCC-GY4 antibodies had very similar binding profiles, with IC₅₀ values of 0.80 μg/ml and 0.98 μg/ml respectively (FIG. 36). Similarly, the chimeric IgG4-GY5 and murine KFCC-GY5 antibodies also had very similar binding profiles, with IC50 values of 0.40 μg/ml and 0.49 μg/ml respectively (FIG. 37). Therefore, the correct variable region sequences for the parent murine monoclonal antibodies were identified and cloned.

Binding affinities were also determined using Biacore system Bia T-100. Both chimeric KFCC-GY4 and KFCC-GY5 antibodies were determined to have higher binding affinities for PLVAP than their respective parent mAbs (Table 8). The two chimeric monoclonal antibodies derived from KFCC-GY4 and KFCC-GY5 are also referred to herein as CSR01 and CSR02, respectively.

TABLE 8 Binding affinities of KFCC-GY4, KFCC-GY5, chimeric KFCC-GY4 (CSR01) and chimeric KFCC- GY5 (CSR02) monoclonal antibodies. Antibody ka (1/Ms) kd (1/s) Kd (M) GY4 1.51 × 10⁴ 7.01 × 10⁻³ 4.64 × 10⁻⁷ Chimeric GY4 5.21 × 10³ 2.12 × 10⁻³ 4.06 × 10⁻⁷ (CSR01) GY5 6.93 × 10³ 4.14 × 10⁻⁴ 5.98 × 10⁻⁸ Chimeric GY5 3.07 × 10⁴ 3.01 × 10⁻⁵ 9.78 × 10⁻¹⁰ (CSR02) ka: association rate; kd: dissociation rate; Kd: dissociation constant (binding affinity).

Example 8 Production and Characterization of Fully Humanized Antibodies that Specifically Bind PLVAP Materials and Methods Overview

Three different kappa light chains and two different heavy chains were constructed based on the cDNA sequences from chimeric KFCC-GY4 (CSR01) antibody. They were used to transfect NSO cell line for production of humanized composite antibodies. Five different cell lines were generated for production of five monoclonal antibodies. Similarly, two different kappa light chains and two different heavy chains were constructed based on cDNA sequences from the chimeric KFCC-GY5 (CSR02) antibody. Four cell lines that produce four different monoclonal antibodies were obtained. The nucleotide sequences of the variable domains of these humanized heavy and light chains are summarized in FIGS. 38A-E and 39A-D. A flowchart for derivation of chimeric antibodies and fully humanized composite antibodies are outlined in FIG. 40.

Abbreviations

Abbreviation Description BLAST Basic Local Alignment Search Tool CDR Complementarity Determining region of an antibody variable region (numbered CDR1-3 for each of the heavy and light chains, as defined by Kabat). Ec(0.1%) The absorbance of a 1 mg/ml solution of protein ELISA Enzyme linked immunosorbent assay FW Framework region - scaffold region of a variable domain supporting the CDRs HRP Horse-radish Peroxidase IgG Immunoglobulin G mAb Monoclonal antibody MHC Major histocompatibility complex OD280nm Optical density measured at 280 nm PBS Phosphate-buffered saline TMB 3,3′,5,5′-tetramethylbenzidine V-region Variable region of an antibody chain P protein PLVAP protein

Design of Human Antibody Variable Region Sequences

Structural models of the mouse KFCC-GY4 and KFCC-GY5 variable (V) regions were produced using Swiss PDB and analysed in order to identify important “constraining” amino acids in the mouse V regions that were likely essential for the binding properties of the antibody. Residues contained within the CDRs (using both Kabat and Chothia definitions), together with a number of framework residues, were considered to be important. Both the VH and VK sequences of KFCC-GY4 and KFCC-GY5 contain typical framework residues. Whereas the CDR 1 and 2 motifs of both antibodies are comparable to many murine antibodies, it was noted that the VH CDR3 for both antibodies are unusually short. From the above analysis, it was considered that composite human sequences of both KFCC-GY4 and KFCC-GY5 could be created with a wide latitude of alternatives outside of CDRs, but with only a narrow menu of possible alternative residues within the CDR sequences. Preliminary analysis indicated that corresponding sequence segments from several human antibodies could be combined to create CDRs similar or identical to those in the mouse sequences. For regions outside of and flanking the CDRs, a wide selection of human sequence segments were identified as possible components of the novel human antibody variable regions.

Epitope Avoidance and Design of Variants

Based upon the above analysis, a large preliminary set of sequence segments that could be used to create both KFCC-GY4 and KFCC-GY5 human antibody variants were selected and analysed using iTope™ technology for analysis of peptide binding to human MHC class II alleles, and using the TCED™ (T Cell Epitope Database) of known antibody sequence-related T cell epitopes (Antitope Ltd.; Cambridge, UK). Sequence segments where significant non-human MHC class II binding peptides were identified, or scored significant hits against the TCED™ were discarded. This resulted in a reduced set of segments, and combinations of these were again analysed, as above, to ensure that the junctions between segments did not contain potential T cell epitopes. Selected segments were then combined to produce heavy and light chain variable region sequences for synthesis. For each antibody, five heavy chains and three light chains were constructed with sequences as detailed in FIGS. 41A-E and 42A-C (for KFCC-GY5) and FIGS. 43A-E and 44A-C (for KFCC-GY4) and sequence alignments as detailed in FIGS. 45 and 46.

Construction, Expression and Purification of Variant Antibodies

Initial variant 1 human antibody VH and VK region genes were synthesized for KFCC-GY4 and KFCC-GY5 using a series of overlapping oligonucleotides that were annealed, ligated and PCR amplified to give full length synthetic V regions. Subsequent human antibody sequence variants were constructed using long overlapping oligonucleotides and PCR, using the initial variant 1 as the template. The assembled variants were then cloned directly into the pANT expression vector system (Antitope, Ltd.; Cambridge, UK) for IgG4 heavy chains and kappa light chains. All combinations of composite heavy and light chains (i.e. a total of 15 pairings) were stably transfected into NS0 cells via electroporation and selected using 200 nM methotrexate (Sigma Catalogue No. M8407-500MG). Methotrexate resistant colonies for each construct were tested for IgG expression levels and the best expressing lines were selected and frozen under liquid nitrogen. IgG4 Variants for KFCC-GY4 and KFCC-GY5 were purified from cell culture supernatants on a Protein A sepharose column (GE Healthcare Catalogue No. 110034-93) and quantified by OD280 nm using an extinction coefficient, Ec(0.1%), based on the predicted amino acid sequence (Table 9). Greater than 2 mg of antibody was purified and analysed by SDS-PAGE (FIGS. 47A,B). Bands corresponding to the predicted sizes of the heavy and light chains were observed with no evidence of any contamination.

TABLE 9 Ec(0.1%) values for KFCC-GY4 and KFCC-GY5 antibody variants Variant Ec_((0.1%)) GY4 Chimera 1.48 GY4 Variants (all) 1.49 GY5 Chimera 1.33 GY5 Variants VH4/VK2 1.33 VH5/VK2 GY5 Variants VH4/VK3 1.35 VH5/VK3

In addition, CHO-K1 cells were transiently transfected using Lipofectamine 2000 (Invitrogen # 11668-019). 72 hours after transfection, cell media was harvested for antibody purification. Briefly, IgG4 human antibody variants from transient transfections were purified from cell culture supernatants on a Protein A sepharose column (Sigma Catalogue No. P3391-1.5G) and quantified using an Fc capture/kappa chain detection ELISA (Sigma Catalogue No. 16260 and A7164) against a human IgG4/kappa standard (Sigma Catalogue No. 14639). A broad observation was that the number of expressing NS0 clones was significantly lower for KFCC-GY4 lineage clones when compared to KFCC-GY5 lineage clones. Furthermore, it was also noted that both stable and transient yields were lower for KFCC-GY4 lineage clones compared to KFCC-GY5. In some cases, the transient yields from KFCC-GY4 lineages were not sufficient to allow complete characterization of the variants and so all subsequent analysis was carried out using NS0 purified material from stable cell lines.

Binding of the Variant Antibodies to Recombinant PLVAP Protein

The binding of KFCC-GY4 and KFCC-GY5 human antibody variants to recombinant PLVAP was assessed in a competition ELISA. A dilution series of variant or control antibody from 30 μg/ml to 0.014 μg/ml (final concentration) was premixed with a constant concentration of biotinylated murine KFCC-GY4 (0.3 μg/ml, final concentration), or from 10 μg/ml to 0.004 μg/ml (final concentration) was premixed with a constant concentration of biotinylated murine KFCC-GY5 (0.1 μg/ml, final concentration), before incubating for 1 hour at room temperature on a Nunc Immuno MaxiSorp 96 well flat bottom microtitre plate (Fisher Catalogue No. DIS-971-030J) precoated with 1 μg/ml recombinant “protein P” diluted in PBS. The binding of the biotinylated mAb was determined by detection with streptavidin-HRP and TMB substrate. After stopping the reaction with 3M HCl, absorbance was measured at 450 nm on a Dynex Technologies MRX TC II plate reader and the binding curves of the test antibodies compared against the mouse reference standard.

Titration of PLVAP Binding by Chimeric and Fully Humanized Composite Anti-PLVAP Monoclonal Antibodies

Each well of an ELISA plate was coated with 50 μl 2.5 μg/ml recombinant PLVAP protein in PBS. After washing and blocking, each well was incubated with a different concentration of humanized monoclonal antibody (0.5 μg/ml to 0.0025 μg/ml) for 60 minutes at room temperature. The binding of the antibody to PLVAP was measured using alkaline phosphatase conjugate of mouse anti-human IgG4 monoclonal antibody (BD Pharmingen) diluted 1000×.

Results

The five lead variants of IgG4-GY4 and murine KFCC-GY4 antibodies have very similar binding profiles (FIG. 48). Absolute IC50 values and values relative to the KFCC-GY4 mAb for the five lead variants are shown in Table 10. All of the lead variants shown are within two-fold of the original murine monoclonal antibody.

Similarly, the four lead variants of IgG4-GY5 and murine KFCC-GY5 antibodies have very similar binding profiles (FIG. 49). Absolute IC50 values and values relative to the KFCC-GY5 mAb for the five lead variants are shown in Table 11. All of the lead variants shown are within two-fold of the original murine monoclonal antibody.

TABLE 10 IC50 Values of KFCC-GY4 Composite Human Antibody ™ Variants IC₅₀ (ratio compared Antibody IC₅₀ (μg/ml) to GY4 mAb) GY4 mAB 1.82 1 VH4/VK2 2.53 1.39 VH4/VK3 2.94 1.61 VH5/VK1 2.18 1.20 VH5/VK2 1.91 1.05 VH5/VK3 2.82 1.55 GY4 Composite Human Antibody™ variants were purified from NS0 stably transfected supernatant and tested in a competition assay with biotinylated KFCC-GY4 mAb. IC₅₀ values are displayed and are also normalized against the binding of the reference KFCC-GY4 mAb.

TABLE 11 IC50 Values of KFCC-GY5 Composite Human AntibodyTM Variants IC50 (ratio compared Antibody IC50 (μg/ml) to GY5 mAb) GY5 mAB 0.38 1 VH4/VK2 0.56 1.47 VH4/VK3 0.43 1.13 VH5/VK2 0.60 1.58 VH5/VK3 0.41 1.08 GY5 Composite Human Antibody™ Variants were purified from NS0 stably transfected supernatant and tested in a competition assay with biotinylated KFCC-GY5 mAb. IC₅₀ values are displayed and are also normalized against the binding of the reference KFCC-GY5 mAb

Composite humanized antibodies derived from chimeric KFCC-GY4 and KFCC-GY5 antibodies were able to bind to PLVAP protein (FIG. 50). Fully humanized composite antibodies from chimeric KFCC-GY4 (CSR01) bind less well than chimeric CSR01. In contrast, fully humanized composite antibodies from chimeric KFCC-GY5 (CSR02) bind more or less equally well as chimeric CSR02.

To confirm that the fully humanized antibodies from KFCC-GY4 (CSR01) and KFCC-GY5 (CSR02) can bind to PLVAP without interfering with the binding of each other, an in vitro enzyme linked immunoassay (ELISA) was performed to show that some of the fully humanized composite antibodies from CSR01 and CSR02 are indeed additive in binding to PLVAP (FIG. 30).

Binding of the humanized antibodies to PLVAP proteins expressed on human umbilical cord vascular endothelial cells was assessed by immunofluorescence studies. All humanized antibodies tested in these studies were able to bind to endothelial cells (FIGS. 51A-C, 52A-G and 53A-E). These results indicate that the humanized antibodies that bind these two epitopes can be used as therapeutic or diagnostic agents independently, or together for their additive effect, if needed.

In summary, the results of the study described in the Examples herein demonstrate that murine monoclonal antibodies can be developed against two different well-defined antigenic epitopes in the extracellular domain of the human PLVAP protein. The amino acid sequences of these two epitopes have been identified. The binding of these antibodies to the two identified epitopes in PLVAP does not interfere with each other and can be additive. Thus, these antibodies, and antibodies derived from them, can be used as therapeutic or diagnostic agents individually or together for their additive effect, if needed. The CDRs responsible for antigen binding have been identified. This information has been successfully utilized to humanize both anti-PLVAP murine monoclonal antibodies for treatment of liver cancer in human subjects and to reduce antigenicity.

Example 9 Development of a Diagnostic Assay for Detecting PLVAP Levels in Serum Materials and Methods PLVAP ELISA

-   -   1. Each well of an ELISA plate was coated with 50 μl KFCC-GY4         mAb at 5 μg/ml overnight. The antibody was prepared in 1×PBS         buffer containing 0.02% sodium azide.     -   2. After washing each well with 200 ul washing buffer (PBS         containing 0.05% Tweenn-20) three times, each well was blocked         with 200 μl blocking buffer (washing buffer containing 2% bovine         serum albumin) for 30 minutes at room temperature.     -   3. Wells were washed three times after blocking.     -   4. 50 μl PLVAP standards and diluted serum samples were added         into designated wells in duplicates and incubated for 60 minutes         at room temperature. Standards and serum samples were diluted in         blocking buffer.     -   5. Wells were washed three times and 50 μl of biotinylated         KFCC-GY5 mAb were added at 0.25 μg/ml.     -   6. After incubation for 30 minutes, all wells were washed three         times.     -   7. 50 μl of 2500× diluted Streptavidin-horseradish peroxidase         (Pierce, Inc. catalog#:N100) were added to each well and         incubated for 30 minutes at room temperature.     -   8. After three washes, 100 μl OPD substrate prepared according         to manufacturer's instruction (Sigma, Inc. catalog#: P-6787)         were added and incubated for an optimal duration of time     -   9. The incubation was stopped by adding 50 μl of 0.18M H₂SO₄.     -   10. OD measurements were taken at 570 nm.

Results

Both murine KFCC-GY4 and KFCC-GY5 anti-human PLVAP monoclonal antibodies were used to establish an enzyme-linked immunoassay (ELISA) to measure PLVAP protein concentration in serum. KFCC-GY4 antibody was used to coat an ELISA plate to capture PLVAP protein in serum, and biotinylated KFCC-GY5 antibody was used to detect PLVAP protein captured by the KFCC-GY4 antibody. The recombinant PLVAP protein was used as a reference standard. As shown by the standard curve of the PLVAP ELISA (FIG. 54), the sensitivity for this assay is about 50 ng/ml. When two serum samples from two liver cancer patients were assayed in two dilutions (2× and 4×), both had measurable PLVAP levels (450 ng/ml and 360 ng/nl) and were parallel with the standard curve. No measurable PLVAP was detected in the plasma of two healthy individuals. Therefore, this assay can be used in diagnostic applications to assay PLVAP levels in serum.

The relevant teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 

1-6. (canceled)
 7. A pharmaceutical composition for the treatment of hepatocellular carcinoma in a mammalian subject, comprising the isolated polypeptide of claim 11 and a pharmaceutically-acceptable carrier.
 8. (canceled)
 9. The composition of claim 7, further comprising at least one chemotherapeutic agent.
 10. The composition of claim 9, wherein the chemotherapeutic agent is selected from the group consisting of doxorubicin, cisplatin, mitomycin, 5-fluorouracil, tamoxifen, sorafenib and octreotide.
 11. An isolated polypeptide that specifically binds a protein comprising SEQ ID NO:23, comprising: i) a) at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:66, SEQ ID NO:68, SEQ ID NO:94, SEQ ID NO:96, SEQ ID NO:98, SEQ ID NO:100, SEQ ID NO:102 and a combination thereof; and b) at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO:64, SEQ ID NO:104, SEQ ID NO:106, SEQ ID NO:108 and a combination thereof; or ii) a) at least one heavy chain amino acid sequence selected from the group consisting of SEQ ID NO:74, SEQ ID NO:76, SEQ ID NO:78, SEQ ID NO:80, SEQ ID NO:82, SEQ ID NO:84, SEQ ID NO:86 and a combination thereof; and b) at least one kappa light chain amino acid sequence selected from the group consisting of SEQ ID NO:70, SEQ ID NO:72, SEQ ID NO:88, SEQ ID NO:90, SEQ ID NO:92 and a combination thereof.
 12. The isolated polypeptide of claim 11, wherein the polypeptide is an antibody.
 13. The isolated polypeptide of claim 12, wherein the antibody binds to an epitope that is present in SEQ ID NO:38 or SEQ ID NO:40.
 14. The isolated polypeptide of claim 12, wherein the antibody has a binding affinity (Kd) for a protein comprising SEQ ID NO:23 of about 4.06×10⁻⁷ M. 15-17. (canceled)
 18. The isolated polypeptide of claim 12, wherein the antibody has a binding affinity (Kd) for SEQ ID NO:23 of about 9.78×10⁻¹⁰ M.
 19. (canceled)
 20. The isolated polypeptide of claim 12, wherein the antibody is selected from the group consisting of a monoclonal antibody, a polyclonal antibody, a chimeric antibody, a humanized antibody, a human antibody and an antigen binding fragment.
 21. The isolated polypeptide of claim 11, wherein the polypeptide comprises a label.
 22. The isolated polypeptide of claim 21, wherein the label is selected from the group consisting of a radioactive isotope and a cytotoxic agent.
 23. The isolated polypeptide of claim 11, wherein the polypeptide comprises a human IgG4 heavy chain and a human IgG4 kappa light chain.
 24. A cell of murine hybridoma selected from KFCC-GY4 (ATCC Patent Deposit Designation PTA-9963) and KFCC-GY5 (ATCC Patent Deposit Designation PTA-9964).
 25. (canceled)
 26. An antibody produced by the cell of claim
 24. 27. (canceled)
 28. A method of treating hepatocellular carcinoma (HCC) in a subject in need thereof, comprising administering to the subject a therapeutically effective amount of the isolated polypeptide of claim 11, wherein the isolated polypeptide inhibits an activity selected from the group consisting of tumor formation, tumor growth, tumor vascularization and tumor progression in the liver of the subject.
 29. The method of claim 28, wherein the isolated polypeptide is conjugated to a radioactive isotope, a cytotoxic agent, or a combination thereof.
 30. The method of claim 28, wherein the isolated polypeptide is administered to the subject intra-arterially.
 31. The method of claim 30, wherein the isolated polypeptide is administered to the subject intra-arterially by a procedure selected from the group consisting of hepatic arterial infusion and transarterial chemoembolization (TACE).
 32. The method of claim 28, further comprising administering at least one chemotherapeutic agent.
 33. The method of claim 32, wherein the chemotherapeutic agent is selected from the group consisting of doxorubicin, cisplatin, mitomycin, 5-fluorouracil, tamoxifen, sorafenib and octreotide.
 34. The method of claim 28, wherein the subject is a human. 35-37. (canceled)
 38. The method of claim 28, wherein the polypeptide is delivered to endothelial cells of blood vessels within or surrounding an HCC tumor in the liver of the subject. 39-41. (canceled)
 42. An in vivo method of detecting hepatocellular carcinoma (HCC) in a subject, comprising: 1) administering the isolated polypeptide of claim 11 to the subject by intra-arterial injection, wherein the antibody comprises a radioisotope; 2) obtaining an image of the liver of the subject; and 3) detecting accumulation of the polypeptide in the liver of the subject, thereby detecting HCC in the subject.
 43. The method of claim 42, wherein the subject is a human. 